I have this file:  $ ls -l  store.sh  -rwxr-xr-x   1 root apache    117 Feb  5  2016 store.sh  $ id uid=48(apache) gid=48(apache) groups=48(apache)   I think that I haven't the permission to edit this file but was possible delete and replace the file. How can it be? Can someone explain this behaviour?

The shell session should say everything: I can't delete a file (movie.avi) although I have write permissions. I don't get what the problem is. Have I missed something?  confus@homeserver:/home/narur$ id uid=1000(confus) gid=1000(confus) groups=1000(confus),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),106(lpadmin),117(sambashare),118(debian-transmission),1001(narur)  confus@homeserver:/home/narur$ ll | grep movie.avi  -rw-rw----  1 narur narur 1,4G Jan 11 09:42 movie.avi  confus@homeserver:/home/narur$ rm movie.avi  rm: cannot remove `movie.avi': Permission denied  # # # # SOME INFOS ON MY SYSTEM: confus@homeserver:/home/narur$ lsb_release -dc Description:    Ubuntu 12.10 Codename:   quantal confus@homeserver:/home/narur$ uname -a Linux conserve 3.5.0-21-generic #32-Ubuntu SMP Tue Dec 11 18:51:59 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux


Is there a material which can allow light (or any other EM radiation) to pass through from one side as if it is transparent but its other side reflects light like a mirror?

I am not talking about mirrors, just a plain window made of glass like material. Would it be possible to allow light pass only in one direction but not the other?


I'm listening to  and David mentioned that posts need one reopen vote to be added to the reopen review queue.  He also mentioned that questions almost never get reopened once they're closed.  Should more questions be added earlier to this queue.  I think that after a question is closed, if the original author makes a substantial edit to the question, it should be eligible for reopening.  Should questions that meet this criteria be added immediately to the reopen review queue (before anyone casts a reopen vote)? Notes: Currently people are encouraged to flag a post for a moderator to review once they've edited their closed question, but  this really doesn't happen very much, I'd really like to see this automated so it happens more often, and I'd like to see a bigger cross-section of the community looking at these than just moderators.  Additional note: I know that all the OP has to do is vote for their own question to be reopened for it to be added to the queue, but this doesn't always happen (it requires 250 reputation, and sometimes people just don't do it).  Maybe just automatically casting the reopen vote for them would be enough to implement this?  Or, as Tim Stone suggests in the comments, maybe just letting them know that voting to reopen their own post will place it in a queue for others to review would see more posts added to the queue?

I've noticed in the last couple of days that there have been a few occasions when there's been a sudden surge of questions in the SO "Reopen" review queue.  Normally there's either no questions at all to reopen or at most three or four, and that's still the case, except that for the last couple of days I've gone to the review page and seen about fifty-odd questions in the queue, where just moments before there had been none.  I've gone through the reviews and the questions themselves seem reasonably legitimate (including the occasional audit), so I'm not questioning that... it just seems odd that there would be so many more than usual all of a sudden, and that they'd all appear at once.  Anyone got any insights, or should I just chalk this down as "one of those things"?


Let see if this is the right place...  I installed and have ran Android -x86 on a virtual machine. Everything works great until I have to force dismount the ISO file from the machine, so that it can load from the partition. Whenever I do this, I get the error GRUB Loader Error 17 or 15. It depends. I formatted the partition to ext4, mainly because it doesnt allow me to format in ext3.  Any help will be greatly appreciated!  Thanks again!

I'm trying to install  in VirtualBox but the installation get stuck at Do you want to install boot loader GRUB    Some background:   The VM was created from the Ubuntu 32-bit (x86) VirtualBox template The VM has 1 core + 3096 MB RAM Video memory: 32 MB PAE/NX enabled Hardware virtualization: both VTx and nested pagination enabled Graphics acceleration: disabled (both 2D and 3D) Storage: 64 GB attached to IDE virtual controller (was SATA before: makes no difference)   I've already tried all the "standard" VirtualBox procedure (PAE yes/no; SATA/IDE; no soundcard; no USB; graphics accel. yes/no).  I also tried run the Live CD in VESA mode: like this it starts, but I'd still prefer to install it.


I have been trying to download the grovy main repository for wine and I keep on getting a 404 error on http://ppa.launchpad.net/webupd8team/java/ubuntu. I have been told it is not supported anymore but I can't seem to get wine without it. how can I fix this problem

When updating, I get the following error message:   W: The repository 'http://ppa.launchpad.net/mc3man/trusty-media/ubuntu xenial Release' does not have a Release file.   Here, I find another statement on this error:   This recommends removing certain PPAs; and, I'm not sure if I should do that since it might mean not getting the updates that I need.    Is this what I should do?


What are the benefits of putting stuff on an object's prototype? For example, these two implementations of ChessPiece seem very similar. What are the trade-offs?  Without prototype  var ChessPiece = function(x, y) {   var self = this;   this.x = x;   this.y = y;   this.getNotation = function() {     return 'abcdefgh'[self.x] + '12345678'[self.y];   };       }  var pawn1 = new ChessPiece(1, 0); pawn1.getNotation(); // 'b1';   With prototype  var ChessPiece = function(x, y) {   this.x = x;   this.y = y; }  ChessPiece.prototype.getNotation = function() {   return 'abcdefgh'[this.x] + '12345678'[this.y]; }  var pawn2 = new ChessPiece(1, 1); pawn2.getNotation(); // 'b2'   To me, the most significant difference is that when getNotation is on ChessPiece's prototype, that method is shared by all instances. When it's not on the prototype, there are multiple copies of getNotation. Does this matter? Is there more I am missing?  As an aside, the reason I prefer the first method is because it is cleaner to write everything in a single constructor function, rather than having to declare ChessPiece and then assign each method on separate lines. Is there a way to work around that issue, if the latter is preferred?

What's the difference between  var A = function () {     this.x = function () {         //do something     }; };   and  var A = function () { }; A.prototype.x = function () {     //do something };


I have bought a new HP BS180TX laptop and installed Ubuntu 16.04 LTS and found that the wifi and bluetooth are not working. Wired connection works fine. I ran lspci -knn | grep Net -A3; rfkill list and the result I got is  03:00.0 Network controller [0280]: Realtek Semiconductor Co., Ltd. Device [10ec:d723]     DeviceName: WLAN     Subsystem: Hewlett-Packard Company Device [103c:8319] 2: hci0: Bluetooth     Soft blocked: no     Hard blocked: no   What should I do?  Solved The  resolved my issue. The first one did not work because the kernel version was not compatible. This even works in Ubuntu 18.04. I have tested this.   Bluetooth issue also fixed by the help of   In 18.04, the kernel update can disable wifi. So you will have to redo the steps in the above answer I mentioned to re-enable it.

How do I install Wi-Fi drivers for Realtek RTL8723DE device in Ubuntu 16.04?  lspci -v | grep -i network 02:00.0 Network controller: Realtek Semiconductor Co., Ltd. Device d723


Using Windows 10, I prefer to treat all folders as "General Items" and use Detail view.  When I create a new folder containing only a few WAV files, the folder optimization automatically changes to "Music".  Similarly, if I create a folder containing a few video clips, it changes to "Videos".  How can I prevent this?  I'm not talking about libraries.  This affects even folders on a secondary hard drive.

I have an empty folder with regular details view. File name, file size, file type columns are shown and I am happy.   Then I put some MP3 or WAV files in. Windows Explorer "kindly" changes the column types. It will show Genre, media length, Album and other metadata tags, but does not show the file size anymore. If I do not like it, I have to manually change the columns back. It is very irritating.  How can I turn this automatic behavior off?


Is there a file that contains the option of the GRUB2 menu that was chosen for the current boot? This question is different from obtaining the Kernel boot sequence, for example, to differentiate two boot options with the same boot sequence.

In the grub.conf configuration file I can specify command line parameters that the kernel will use, i.e.:  kernel /boot/kernel-3-2-1-gentoo root=/dev/sda1 vga=791   After booting a given kernel, is there a way to display the command line parameters that were passed to the kernel in the first place? I've found sysctl,  sysctl --all   but sysctl shows up all possible kernel parameters.


I do not want to use XeLaTeX or LuaLaTeX, can I use the Arial font anyway?  According to  the Arial font can be used when using XeLaTeX or LuaLaTeX. When I use XeLaTeX I get new problems like my copyright signs are not recognized. What can I do?

In preamble, I have:  \renewcommand{\familydefault}{\sfdefault} \usepackage{arial}   but it doesn't work.  How do I set my font to Arial throughout the entire document?  UPDATE:  In short, both answers work.  It really depends on the environment. If using LaTeX and don't mind using a cloned font then choose Herbert's answer. If using XeLaTex and want to use the authentic font then choose Leo's.


The order of $GL_2 (\mathbb{Z}/p)$ seems to be $(p^2 - 1)(p^2 - p)$ using the fact stated in  Wiki page.  Quoting a line from there :     This can be shown by counting the possible columns of the matrix : the first column can be anything but the zero vector; the second column can be anything but the multiples of the first column; and in general, the $k$ th column can be any vector not in the linear span of the first $k − 1$ columns   I know that the the number of distinct (unordered) bases of an $n$-$\text{dim}$  vector space over $\mathbb{F}_p$ is $\frac{(q^n - 1)\cdots (q^n - q^{n-1})}{n!}$ (call this Lemma $1$). I have an understanding of its proof as well.  I am not very much aware of matrices and I have not worked with them.   $\color{red}{[1]}$ How do I prove this using the Lemma $1$ stated above (and/or using the strategy written on the wiki article)?  $\color{red}{[2]}$ It appears that $\left\{\begin{pmatrix} 1 & 0\\ 0 & 0 \end{pmatrix} , \begin{pmatrix} 0 & 1\\ 0 & 0 \end{pmatrix}, \begin{pmatrix} 0 & 0\\ 1 & 0 \end{pmatrix}, \begin{pmatrix} 0 & 0\\ 0 & 1 \end{pmatrix} \right\}$ forms a basis of $GL_2(\mathbb{Z/p})$ which makes it $4$-$\text{dim}$. Why do we work with $n=2$ for this then?

I need to find $|GL_2(F_p)|$, I am very very uncomfortable in counting, so please help here I proceed,  $\begin{pmatrix}a&b\\c&d\end{pmatrix}$ be such an invertible matrix, so we need and sufficient that $ad\neq bc$, so if i chose all non zero $a,b,c$ arbitrarily and chose $d\neq a^{-1}bc$ and form matrices then the cardinality   will be $(q-1)^3\times (q-2)$, well now if one of $a,b,c,d$ be zero then other three can be anything nonzero so in this case cardinality will be $4(q-1)^3$, so finally if two entries are $0$ then they must be opposite to each other i.e diagonally, but other two must be nonzero, so cardinality in that case $2(q-1)^2$, so total number is just sum of three cases.


I trying to fetch data form database which is have 3 column unique_id, parent_id & node_name, but this query (Given in below) is return only two rows.  Condition: every parent has two child.  DROP PROCEDURE `treeTbl`; CREATE DEFINER=`bizsol`@`localhost` PROCEDURE `treeTbl`(IN `childId` INT(255)) DETERMINISTIC NO SQL SQL SECURITY DEFINER BEGIN  DECLARE tempId INT DEFAULT 0;  SELECT *, unique_id as id FROM t_users WHERE 1 AND parent_id = childId;  IF(tempId>0)   THEN     SET tempId = id;     CALL treeTbl(tempId);  END IF; END   And call form here,  CALL treeTbl(3);

note: this question has been updated to reflect that we are currently using MySQL, having done so, I would like to see a how much easier it would be if we switched to a CTE-supporting database.  I have a self-referencing table with a primary key, id and a foreign key parent_id.  +------------+--------------+------+-----+---------+----------------+ | Field      | Type         | Null | Key | Default | Extra          | +------------+--------------+------+-----+---------+----------------+ | id         | int(11)      | NO   | PRI | NULL    | auto_increment |  | parent_id  | int(11)      | YES  |     | NULL    |                |  | name       | varchar(255) | YES  |     | NULL    |                |  | notes      | text         | YES  |     | NULL    |                |  +------------+--------------+------+-----+---------+----------------+   Given a name, how can I query the top-level parent?  Given a name, how can I query all of the id's associated with a record of name = 'foo'?  context: I am not a dba, but am planning to ask a dba to implement this type of hierarchical structure and would like to test some queries. The motivation for doing so is described by .    Here is an example of the relationships among ids in the table:    -- ----------------------------------------------------- -- Create a new database called 'testdb' -- ----------------------------------------------------- SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0; SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0; SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='TRADITIONAL';  CREATE SCHEMA IF NOT EXISTS `testdb` DEFAULT CHARACTER SET latin1 COLLATE latin1_swedish_ci ; USE `testdb` ;  -- ----------------------------------------------------- -- Table `testdb`.`observations` -- ----------------------------------------------------- CREATE  TABLE IF NOT EXISTS `testdb`.`observations` (   `id` INT NOT NULL ,   `parent_id` INT NULL ,   `name` VARCHAR(45) NULL ,   PRIMARY KEY (`id`) ) ENGINE = InnoDB;  SET SQL_MODE=@OLD_SQL_MODE; SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS; SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS;  -- ----------------------------------------------------- -- Add Example Data Set -- -----------------------------------------------------   INSERT INTO observations VALUES (1,3), (2,5), (3,NULL), (4,10),     (5,NULL), (6,1), (7,5), (8,10), (9,10), (10,3);


I'm looking for a word that means "doing lots of work but in vain"  the amount of work done is a lot, but the results obtained is very small.

I'm an American living in the Netherlands who is learning Dutch. There's an idiom in Dutch that describes performing a needless/futile activity, "water naar de zee dragen," which literally translates to "carrying water to the sea." My Dutch parents-in-law asked me if there was an English equivalent, but I couldn't think of one.  In doing   , I found that the English translation given for the this idiom is always "carrying coals to Newcastle." This was the first time I'd ever come across the phrase, and subsequent searches revealed that it was indeed of  , though one site I found did . However, neither I nor any of my culturally American friends have ever heard of this phrase.   Is there an American English idiom or phrase that carries the same connotations for carrying out a futile activity?


I have a speaker adapter, with an output rating of AC 11.5V ~ 1600mA, which I am looking to replace and the only replacement I can find has a rated output of 12V ~ 2000mA.   I've read somewhere that a higher current is okay since the speakers will only draw what it needs, but I'm wary if the 0.5 difference in voltage will overload/damage it.

Power supplies are available in a wide range of voltage and current ratings.  If I have a device that has specific voltage and current ratings, how do those relate to the power ratings I need to specify?  What if I don't know the device's specs, but am replacing a previous power supply with particular ratings?  Is it OK to go lower voltage, or should it always be higher?  What about current?  I don't want a 10 A supply to damage my 1 A device.


What i want to do is to change the class of the div tag with a toggle button using javascript. So that when i press the button once the div tag gets the show class, and when i press the same button again it gets the hide class. Is this possible?  html:  Show/hide
     I want this div to toggle between the 'show' class and the 'hide' class
   css:  .show {     display: block; }   .hide {     display: none; }   js:  function toggle(){     var hide = document.querySelector(".hide");     var show = document.querySelector(".show");  }  var hidebutton = document.querySelector(".togglebutton"); hidebutton.onclick = toggle   Would document.getElementById("MyId").className = "MyClass"; be usable somehow?

How can I change the class of an HTML element in response to an onclick or any other events using JavaScript?


This is the file.  scr  PI Name: RRC Access Failures due to UU, Value: 0.13394141 prog PI Name: RRC Access Failures due to UU, Value: 0.16077702 sch PI Name: RRC Access Failures due to UU, Value: 0.11781933   I want to search Failures and remove the remaining strings in that line.  My output should be,  scr  PI Name: RRC Access Failures prog PI Name: RRC Access Failures sch PI Name: RRC Access Failures   I tried sed command, but it is deleting entire line.  Any suggestions?

I'm trying to use sed to remove the rest of a line after:  HTTP1.1" 200  I can't figure out how to get sed to understand I want that whole thing as a string to match, including the double quote and the space.  An example for good measure, I want to turn:  "GET /images/loading.gif HTTP/1.1" 200 10819 "https://...   into   "GET /images/loading.gif HTTP/1.1" 200


Question: Find the equation of the form ax+by+cz=d whose graph is the plane through the origin gneerated by <4,-1,2> and <-1,0,4>.  I'm not sure where to start, and I don't whether to use cross and dot product.

Given two vectors $u,v\in\mathbb{R}^3$, find the parametric equations for the plane through the origin parallel to $u$ and $v$.  I'm having a difficult time understanding this question. How can a plane through the origin in $\mathbb{R}^3$ be parallel to two vectors, both of which start from the origin? Surely they all intersect at the origin and thus not parallel?  More concretely, $u=(1,2,3)$ and $v=(-2,1,1)$. The cartesian equation of the plane is $x+7y-5z=0$, which is essentially the solution. But I want to know why.


Storing the patient class value in Hashmap like this.  { 0=Patient [patientName=Robert, phoneNumber=9878594302, age=30],  1=Patient [patientName=mathew, phoneNumber=9876643278, age=56],  2=Patient [patientName=smith, phoneNumber=87, age=8334456781] }   Based on age, want to display the descending and ascending order of the hash map value?  how is it possible ?

I am relatively new to Java, and often find that I need to sort a Map<Key, Value> on the values.  Since the values are not unique, I find myself converting the keySet into an array, and sorting that array through array sort with a custom comparator that sorts on the value associated with the key.  Is there an easier way?


Let $f \in \mathcal{L}^1(\mathbb{R})$. Is it true, that for almost all $x \in \mathbb{R}$ we have  $$\lim_{n \rightarrow \infty} f(x + n) = 0?$$  I was already able to prove that we have  $$\lim_{n \rightarrow \infty} \int_{[n, n+1]} f(x) \,d\mu(x) = 0$$  (using dominated convergence). How can I proceed from here?

I want to show that for $f: \mathbb{R} \rightarrow\mathbb{R}$ Lebesgue integrable  $\displaystyle{\lim_{n \to +\infty} f(x+n) =0}$ almost everywhere.  It is clear to me that this statement is true and I have tried to prove it by contradiction, by assuming that either $\displaystyle{\lim_{n \to +\infty} f(x+n) =\infty}$ or$\displaystyle{\lim_{n \to +\infty} f(x+n) =K}$ with $K\in \mathbb{R}$ .  In the first case  we can follow that $|f|=\infty$ so that $\int_\mathbb{R}f=\infty$ and we have a contradiction.  In the other case we know that there must be an $a\in \mathbb{R}$ so that $\forall x>a$ we have $f_+(x)>K/2$ and by that:  $\int_{{\mathbb{R}}+}|f|>\int_{\mathbb{R}_+}f_+=\int_{[0,a]}f_++ \int_{(a,\infty)}f_+>\int_{[0,a]}f_++\int_{(a,\infty)}K/2=\infty$  Would this be enough to show the statement? Can I even make the assumption that the limit of $f(x+n)$ "exists"? Any hints would be great.


I am trying to estimate the (say 95%) confidence interval of a proportion. For instance, I want to estimate how many students will take a particular course next year. There are N1 students in total. I asked randomly N2 students, and N3 students say yes. I estimate the proportion is N3/N2. I tried to estimate the confidence interval as:  Source:  However, if p' is 0 or 1, how could I calculate the standard deviation because it will become 0, regardless of the sample size?

What is the best technique to calculate a confidence interval of a binomial experiment, if your estimate is that $p=0$ (or similarly $p=1$) and sample size is relatively small, for example $n=25$?


Can anyone please guide me on how to enable root login in Ubuntu 17.04?

I would like to enable the root account on my Ubuntu installation.  I realize the security implications of this.


How do reviewers/referees make sure that the author has done the work as he described in his paper and the written results are achieved?  Do they ask for the code or the tools that you have used? Will they test the output to make sure that the results are not faked?   I know that reviewers with 20+ years experience in the specific field can figure out if the results are real or fake or if they are even accomplishable, but it is still easy for the writer to fake results without any monitors..   For example in CS machine learning, you can extract an extra feature from the texts and claim that you got better results in classification than others have done before, when in reality you did not. So how do reviewers make sure that your work is sincere?

I am preparing a paper in the field of Computer Science.  In order to report test results, we usually run a number of tests and report the average of those tests.  For each test, we generate random data.  Because of the randomness, at some points, the results may come out not as expected.  For instance, a graph may be like:   Usually, one should explain why on points 8, 11 and 12 there is a decrease on the plot. Probably, it is because of that randomness.  Not hand-crafting all the graph, but just manipulating a few points makes the graph acceptable:   Since three weeks or so, I work my ass off and try to figure out why my resulting graph looks like the first one. Sometimes I feel like yielding to temptation and just modify the raw data before I go crazy.  I believe, at this point the title became misleading, so let me make it clear:  I am not seeking an advice on data manipulation. I will not manipulate my data. However, I ask to myself "how the hell this can be detected?"  And now, I don't only ask to myself, but to whole community. How is this detected? For editors, referees out there, have you ever detected something like this?


I don't know a thing about LaTex, but I grab this bash script from the internet to convert .c and .h file to PDF.  I would like to change the font, or at least make it bigger.   Here's the code :   #!/usr/bin/env bash  tex_file=$(mktemp) ## Random temp file name  cat<<EOF >$tex_file   ## Print the tex file header \documentclass{article} \usepackage{listings} \usepackage[usenames,dvipsnames]{color}  %% Allow color names \usepackage{courier} \lstdefinestyle{customasm}{   belowcaptionskip=1\baselineskip,   xleftmargin=\parindent,   language=C,   %% Change this to whatever you write in   breaklines=true, %% Wrap long lines   basicstyle=\footnotesize\ttfamily,   commentstyle=\itshape\color{Gray},   stringstyle=\color{Black},   keywordstyle=\bfseries\color{OliveGreen},   identifierstyle=\color{blue},   numbersep=100pt,   showspaces=false,   showstringspaces=false,   xleftmargin=-8em, } \lstset{    basicstyle=\fontsize{25}{13}\selectfont\ttfamily }  \usepackage[colorlinks=true,linkcolor=blue]{hyperref} \begin{document} \tableofcontents  EOF  find . -name "*\.c" -o -name "\.h" | sed 's/^\..//' | sed 's/^\..//' |                 ## Change ./foo/bar.src to foo/bar.src  while read  i; do                ## Loop through each file    echo "\newpage" >> $tex_file   ## start each section on a new page   echo "\section{$i}" >> $tex_file  ## Create a section for each file    ## This command will include the file in the PDF   echo "\lstinputlisting[style=customasm]{$i}" >>$tex_file done && echo "\end{document}" >> $tex_file && pdflatex $tex_file -output-directory . && pdflatex $tex_file -output-directory .  ## This needs to be run twice                                            ## for the TOC to be generated   I've tried to add the line   \lstset{    basicstyle=\fontsize{25}{13}\selectfont\ttfamily }   and add :   numbersep=100pt,   to change the font size, but nothing happened. Any help would be greatly appreciated!

Which book (free or otherwise) was the most useful to you when you started learning LaTeX?  I am frequently asked this question by friends who want to learn LaTeX, and I recommend the book which got me started, , but I feel that there might be better options around.  Also see .


I am coding a page (for internal use at my company) to try and trigger "one click" browser based video conferencing. We use a web based video conferencing solution (www.bluejeans.com). Currently to start a video session, the user navigates to a url (www.bluejeans.com/, and logs in. We use this with a camera and projector, so the user then needs to drag the browser window onto the projector screen, maximise the window, and hit F11 to remove the browser gubbins.  I want to streamline the process to the user clicks a link, and the new browser window is opened at the correct link, maximised, moved to the correct screen and "F11'd" (browser bars etc removed).  The application is a c# web application, but I assume I'll need to use javascript for this client side window manipulation. I can get a window to open maximised, but can not make it remove the border / address bar.  Having read round it looks like it's for security reasons, which makes sense. However, given that I'm in a "closed" environment, I wonder if there's any other approach I could use? For example a Windows Forms app to trigger a new window?  Edit:  This is different to other questions I have seen that resize the content within the browser to make specific elements full screen. In this case I want to interact with the browser itself, hiding the toolbars and simulating an F11 keypress.

I want to run a psychological study for which participants have to look at large images.  The experiment is done on the web and therefore in a browser window. Is it possible to tell the browser to go into fullscreen, for example on button press?  I know there is the possibility to open a fixed-size popup window. Do you think this would be a feasable alternative? And if, what would be the best way to do it? Are there elegant ways of detecting a popup-blocker, to fallback and run the study in the original browser window.  The main concern is that the participants of this study are not familiar with technical details and should not be bothered by them.


I want to find the following integral: $$\int_0^{\infty} \frac{1}{(1+x^n)(1+x²)}.$$ I enter small values of $n$ on Wolfram and it seems like the answer should be $\pi /4$. Can anyone confirm this for any $n$? I try to do fraction decomposition but it gets ugly really fast. (I think this should have been answered somewhere but I really can’t find it. Apologize in advance if this is a duplication)

Let $a$ be a non-zero real number. Is it true that the value of $$\int\limits_0^\infty \frac{\mathrm{d} x}{(1+x^2)(1+x^a)}$$  is independent on $a$?


I have two cylinders $x^2 +  y^2=a^2$ and $x^2+z^2=a^2$. I need to find the volume common to both of them. Now, I know that one of them has axis along $z$ axis and the other has it along $y$ axis. I am having trouble in visualising the limits of $x$ and $y$.  The $z$ must be enclosed within $0$ to $a$ and maybe y between $-a$ to $a$. Please help in evaluating the limits for $x$ portion

Find the volume common to two circular cylinders, each with radius r, if the axes of the cylinders intersect at right angles. (using disk/washer)  I saw no example of this problem anywhere.. I saw an example how to solve it without calculus but I'm afraid that'll be deductions on my test.. I have the volume of a cylinder and the method of area between two curves but this is out of my reach.... I don't know what I can try...


This question is based on the equation above, where for all integers $y$, if $\gcd(9,y) = 3$, then $\gcd(9,y^2) =9$.  I know this statement is true as if you try to put whatever that is a multiple of 3 as $y$ and if the value matched with the first condition where the $\gcd$ is $3$, it'll match the second condition. For example, if $y = 3,6,12,15,18,21,24...$ they will all work for both conditions.  What I'm trying to know now is how do I put into words to explain how they actually work in pair? More specifically, I am trying to understand the logic behind how they work for each other.

How to prove $\gcd(a^2, b^2) = (\gcd(a, b))^2$?  My attempt:  Let $\gcd(a, b) = d$.  Then $d|a$ and $d|b$ then $d^2|a^2$ and $d^2|b^2$. i.e $d^2$ divides $a^2 ~~\&~~ b^2$.


Background: My Hill-dwarf character started out as a barbarian.  When his clan battled the undead hordes, he barely escaped with his life.  He was taken in by a druid, and discovered a higher calling.  Druid society is a contradiction in terms, except its not, because druidcraft and druidic exist.  They aren't normal norms, but they exist.  He grew up to his current level, and was sent "walkabout".  He has strength, but he is also a bit naive.  So he is out adventuring, trying to be meaningful in the world. The problem: I'm trying to figure out what his role in battle is.  Back-line (heals, spells), front-line (tank, ...), or what?  In our game (Storm Kings Thunder?) we are going up against giants.  We took on a pair of fire giants.  We took on a half-dozen hill giants.  Those things lay out damage, and wild-shape doesn't seem up-to-par.  I'm trying hard to not die. The question: Does the barbarian unarmored defense, which is class and not race based, which adds dex bonus and con bonus to race base AC, apply to wild shape? Thoughts: There is an argument to be made that non-hominid forms might have a very different unarmored defense than anthropomorphic forms.  An effective unarmored defense for a dire wold might look very different from, and be non-intuitive to a non-wolf. Possibly related questions:    (The 10 is the base AC for human/dwarf/elf.  A wild-shape creature, such as a wolf, has a higher base AC.  Why would the wild shape bonus for a base human AC apply?  If the wolf has higher dex, for instance, and the character in that form is more capable of exploiting it than a base creature of that form, which is the essence of unarmored defense, then why would the unarmored be based against 10.)  I'm asking for justification, not just "what is the rule", and in that way my question is meaningfully deeper than the other one.   UPDATED QUESTION: The answer is given that you can choose the best between the creatures or 10 + dex + con. Where does the "10" come from, and why is it the correct base? What    is the "physics" that makes the wild-shaped druid retain the 10? One thinks of the "mean" for (barberian) humanoid AC as 10.  If Dex and Con were bad it would be lower.  If they were great it would be higher.  Why would the "mean" for Spider not be 14?  As a race they are fast, but a slow spider might have lower, while a very fast spider might have higher.

I have a multi-classed Monk/Druid, and let's say I wild shape into a Giant Eagle.  Will I have an AC of 13 (specified in creature statistics), or will I have an AC of 15 (10 + Dex (+3) + Wis (+2))?  Also related, does this depend on if the creature I wild-shape into meets the multiclass requirements for a Monk (Dex of 13+ and Wisdom of 13+)?


I would like to create a regex that ignores accent.  For instance:  string s = "I am an old élephant"; string pattern = "elephant"; bool result = new Regex(pattern, RegexOptions.CultureInvariant).IsMatch(s);   My culture when I test is:  System.Globalization.CultureInfo.CurrentCulture = Fr-fr   So I would have expected this code to find a match but it does not.  Is there an easy way to get a match for this?  I am trying to make a StringReplace overload method that would replace élèphânt with elephant and so on.

I'm trying to convert some strings that are in French Canadian and basically, I'd like to be able to take out the French accent marks in the letters while keeping the letter. (E.g. convert é to e, so crème brûlée would become creme brulee)  What is the best method for achieving this?


I wan to create a user on Ubuntu valid for 10 min. How can I do that if it's possible?

This is what I'd like to be able to do:  After a user's account is created, they should be able to ssh-tunnel, but their account is automatically removed after 30 days unless the countdown is reset by the root user.  How can I automate this? I'll have to handle around 15 users.


Can you plese help me with php fwrite. Csv showing wrong characters  something like:  opÄ‡ĹˇpĹˇÄ‡ĹˇÄ‡Ĺˇp Ä‡pĹˇÄ‡pĹˇÄ‡p ĹˇÄ‡pĹˇÄ‡pĹˇÄ‡  This is php code for input:  I can't find option to fix UTF-8 for this php:     <?php if (isset($_POST['myname'])){ $name = $_POST['myname']; $handle = fopen('names.csv', 'a'); fwrite($handle, $name."\n"); fclose($handle); }  ?>   Html:      <form method="post" action="demo.php">     Myname: <input type="text" name="myname" />      <input type="submit" name="submit" value="submit data" />    </form>   Somebody help please?

I'm setting up a new server and want to support UTF-8 fully in my web application. I have tried this in the past on existing servers and always seem to end up having to fall back to ISO-8859-1.  Where exactly do I need to set the encoding/charsets? I'm aware that I need to configure Apache, MySQL, and PHP to do this — is there some standard checklist I can follow, or perhaps troubleshoot where the mismatches occur?  This is for a new Linux server, running MySQL 5, PHP, 5 and Apache 2.


Let $T\in\mathcal L(V)$. Show that if $T^n=0$, for some $n\in\Bbb N_{>0}$, then $I-T$ is invertible.   I can show that the above is true whenever $\dim V<\infty$, but I dont know how to prove it if $\dim V=\infty$. I dont know where start because nearly all my knowledge of linear algebra is based on finite dimensional spaces.  I though a sketch for a proof by contradiction, assuming that $I-T$ is not invertible but $T^{n-1}\neq 0$ and $T^n=0$ for some $n\in\Bbb N_{>0}$, but I dont know what to do from here because $I-T$ not being invertible doesnt necessarily means that $I-T$ is not bijective (I was thinking to try to reduce the problem to show that $I-T$ is bijective), it can be the case that $I-T$ is bijective but discontinuous, hence not invertible.  Maybe the exercise would need to add that $V$ is finite dimensional, but this is not stated so I assumed that I must show that the statement is true also when $\dim V=\infty$.  Some help will be appreciated, thank you.

So my friend and I are working on this and here is what we have so far.  We want to show that $\exists \, B$ s.t. $(I+A)B = I$. We considered the fact that $I - A^k = I$ for some positive $k$. Now, if $B = (I-A+A^2-A^3+ \cdots -A^{k-1})$, then $(I+A)B = I-A^k = I$. My question is: in matrix $B$, why is the sign for $A^{k-1}$ negative? Couldn't it be positive, in which case we'd get $(I+A)B = I + A^k$?  Thank you.


How do you integrate even powers of sine and cosine? For example, how is $\int\sin^2(x)\ dx$ solved? What about $\int\cos^2(x)\ dx$ or $\int\sin^2(x)cos^2(x)\ dx$ or $\int\sin^2(x)cos^4(x)\ dx$?    I know that when there is an odd function you can use the identity property - but here they are even.  A similar question would be solving tan/sec integrals when they are odd.     I want to show my steps, but I am not even sure where to begin. The only thing I can say is that I saw mention of something called the power reduction formula when reading through other questions - but I never learned it.

Suppose $\displaystyle P(x,y)$ a polynomial in the variables $x,y$.   For example, $\displaystyle x^4$ or $\displaystyle x^3y^2 + 3xy + 1$.  Is there a general method which allows us to evaluate the indefinite integral     $$ \int P(\sin x, \cos x) \text{d} x$$   What about the case when $\displaystyle P(x,y)$ is a rational function (i.e. a ratio of two polynomials)?   Example of a rational function: $\displaystyle \frac{x^2y + y^3}{x+y}$.    This is being asked in an effort to cut down on duplicates, see here:   and here:


I'm trying to install Xubuntu 13.04 on an HP Envy h8-1414 desktop computer running Windows 8. I would like to set it up dual-boot. I downloaded the 64-bit AMD desktop ISO onto a USB device and booted from it. I am able to "try ubuntu" just fine - in fact I am writing this message from within Firefox while trying it. But when I try to install it, the installer shows me this when trying to select a partition, see screen shots here:  (I'd love to show the screen shot inline instead of with a link, but I don't have the 10 reputation points.) I used gparted to carve out some space for Ubuntu, and it shows me the partition list just fine. I also read in other threads on askubuntu that I should try using gdisk to check for errors in the GPT disk. But that seems to show that everything is fine.  I'd love to get xubuntu going on this machine. Thanks in advance for your help!  Sridhar  Edit: I forgot to mention that when I click the buttons in the partition screen on the installer, it crashes.

I'm absolutely new to Linux. I would like to know how to install Ubuntu alongside the pre-installed Windows 8+ OS.  Should I do it with Wubi, or through the Live USB/DVD?  What steps do I need to take to correctly install Ubuntu?


Let's say dividends don't exist, and will NEVER do, for all companies in the world.  What would stocks then be worth?  The stock could be valued according to the book value. Maybe more if the company has any usefulness (for example a media company) for the owner.  Besides that, would stocks have any value at all for the shareholders?  Some people claim that shareholders could still get profits from capital gain, but could there be any capital gain without dividends?  Again: I'm talking about a theoretical situation where absolutely no dividend would ever be paid. It's completely different than not paying dividend for 50 years or so.   Again²: my question is different than the one suggested. Here I assume dividends (or any other form of capital like share repurchase) will never be paid. I know this is not possible in reality, and this is only a theoretical situation. So why am I asking this question? Because some people claim that investors only need to care about the increase of the stock's price. IMO, the price of a stock can't increase if there is no other form of capital gain.  And I should have been more clear about the dividends. What I meant is any form of returning capital to the shareholders. So the shareholders could only get a gain from the increasing stock's price. I believe this is in fact, not possible in the long term (as Chris said in his point 3).  Edit: I wonder if the people who marked it as duplicate even read it..

I read somewhere that companies are not required to pay dividends to shareholders (this is correct, yes?).   If so, then if company A never pays dividends to its shareholders, then what is the point of owning company A's stock? Surely the right to one vote for company A's Board can't be that valuable.   What is it that I'm missing?


I am interested to see how this new statistics motivate users to contribute. But in the data dump, this variable seems not to be in the data dump.

I know the new profile design hasn't been updated for  on the network yet, so maybe this is a bit too early. Nonetheless, please include the "People Reached" data in  at your earliest convenience. Also, I was just made aware that users helpful flag counts are now publicly displayed on their  towards the top-right, underneath the people reached stat. So please include this data in SEDE as well.


Why do I (a non-expert native English speaker) include the definite article here before the country?  Here's a delivery. It's destined for the US. Here's a delivery. It's destined for the UK. Here's a delivery. It's destined for the Republic of Korea. Here's a delivery. It's destined for the Republic of Ireland.   And not here?  Here's a delivery. It's destined for Ireland Here's a delivery. It's destined for Portugal. Here's a delivery. It's destined for Germany. Here's a delivery. It's destined for Western Samoa.

The Punjab is a rich state.   Is it correct to use the before Punjab?


Always wanted a clear explanation as to why these animals had double letters at the beginning of the spelling. What’s up with that?

Usually, when we see two letters put together it is to define the pronunciation or to differentiate synonyms or just its foreign origins. But some words don't seem to have any reason to double up.     Why does vacuum have two of the letter U?  Why does aardvark have two of the letter A?  Why does llama have two of the letter L?


Meaning of pure rolling here: Rolling without slipping. Now moving to the question: In pure rolling there is only one type of force which is static friction which helps to start the pure rolling motion of the body. But I want to know that what will happen after pure rolling, will the body move forever ? as in reality the body stops because nothing is ideal in reality, the tire compresses or even nothing is purely rigid. But in physics we assume them to be ideal. So what will happen after pure rolling is started ? and if it stops how it will stop.

Suppose a wheel is rolling smoothly on a horizontal plane i.e., it is rolling without slipping.  Now let's take the two cases of the horizontal plane:   It has friction It is frictionless   In the first case, as of my knowledge friction doesn't come into play when there is no slipping. So, will the wheel roll forever? If it comes to rest is the answer friction? If not what brings it to rest?  In the second case, there is no friction. So, here also will the wheel roll forever? And if it comes to rest what brings it to rest?


We are in the process of developing Intranet on SharePoint Online for my organization. What are the options available to set up a development environment(On Prem or Azure)? So we dont have to make the changes on the production environment.  Any suggestions are helpful. Thanks

We have one tenant for the company in Sharepoint Online, and we're working in integrating new services. We have got the following piece of advice:  Why not use a DEV tenant to make your changes, and test and avoid problems.  As far as i know, it shoud be:  company.sharepoint.com  company-dev.sharepoint.com  Ok, it seems a good idea, but we aren't sure how to acomplish it. How can i get this scenario?  It would great to have the same accounts in both tenants, but i'm not so sure that it could be possible.  What would be best practices for this scenario?


I have 2 vector line layers. They are subjacent, so one of them is exactly on top of the other but the features have different nodes and attributes.   My goal is to create labels and descriptions for the features which contain attributes from both. The idea is to create a third layer which is split up like the two existing ones and has the attributes from both.   So I want to merge both layers and the result layer should have all the nodes and all attributes.

I have several layers which are stagged on each other. I need to create a label (or text-window / description, doesn't matter) which should contain values from different layers. Creating a regular label I can only choose attributes from this layer. Because the features have different nodes, it is not possible to just merge the layers.


I am travelling to Australia (Adelaide) on PR (E-Visa) 1st time from India (So do i need any transit visa at Hong Kong & at Perth airport if i stay inside the airport only & my time b/n the connecting flights is less than 8 hrs)

I am an Indian national with a valid Indian passport. I intend to travel to San Francisco (US) via Hong Kong with Singapore Airlines and Cathay Pacific. I have to transit through Hong Kong without exiting the airport transit area within 2 hours.  Do I need a transit visa (pre-arrival registration) for Hong Kong for this short duration?


At times, during commentary, commentators speak sentences like "Playing well, Victor is", "A great player, Steven was".

There is a function in Arabic grammar where you may bring forward in sentence order a word - as well as deferring it.  For example: if the sentence order is Subject - Verb - Object, you can bring the object forward to be before the subject,  yielding Object - Verb - Subject or Object - Subject - Verb.  Similarly, if you have Noun Phrase - Verb Phrase, you can move the verb phrase forward so you get Verb Phrase - Noun Phrase.  This is used to add emphasis to the item brought forward. The same applies to moving the item to the end of the sentence.  Is there a grammatical term in English that represents this function or functions?


I am having a heck of a time getting some icons to all appear aligned how I want.  Here is image of situation:    Here is a jfiddle that I set up to try and capture the necessary details:      .topicrow-header .ld-topic-info {     margin-left: 10px; }  .ld-topic-info .fas, .ld-topic-info .far {     padding-left: 10px;     padding-right: 10px; }  .topicrow-header.stick {     position: sticky;     position: -webkit-sticky;     top: 110px;     font-size: 26px;     background-color: #ff9535;     color: white;     font-weight: 300; } .topicrow-header {     z-index: 50;     background-color: #d3d3d380;     margin-top: 6px;     padding: 5px;     margin-left: 0;     font-size: 20px;     color: #007bff; } .row {     display: -ms-flexbox;     display: flex;     -ms-flex-wrap: wrap;     flex-wrap: wrap;     margin-right: -15px;     margin-left: -15px; }  .ldnt-content-notes {     text-align: center;     display:inline; }  .ldnt-content-notes .nt-note-tab {     margin: 0;     display: inline;     color: #fff; }  .nt-note-tab {     display: inline;     text-align: center;     font-weight: bold;     bottom: 0;     text-decoration: none;     border-bottom: 0 !important;     font-size: 14px;     box-shadow: none !important;     transition: all ease-in-out 250ms;     background: rgba(0,0,0,0.95);     z-index: 9000; }

Here is some topic title

     I have tried so many different things but just can't get it right. The first 3 icons are without divs, they are just displayed inline as  elements. The 4th icon has a div and a element as they used by a wordpress plugin. Those elements are somehow causing the problem but I can't figure out how.   I want to have the 4th icon displayed as same size as preceding 3 icons and without that black background as well, but for now just trying to solve the alignment problem so that these 4 icons are aligned with one another with no vertical offsets.  Ideas?  thanks, Brian

I have a div with two images and an h1. All of them need to be vertically aligned within the div, next to each other. One of the images needs to be absolute positioned within the div. What is the CSS needed for this to work on all common browsers?

testing...


Refer to . At the bottom, it says "This question has been asked before and already has an answer." If you look at the duplicate question, it does not have an answer. That is all.

I  here on MSO today, but it was found to have been asked .  I'm not concerned by this (better to be found by more than one user) but, I noticed that the wording in the closure statement is factually incorrect:    No it doesn't have an answer - Not even a sniff of one!  This statement, logically, should be factually accurate and reflect the existence of answers and include singular/plural references to them - or at a minimum use language that covers both scenarios.  Edit: As a result of my question,  and the bug in question has been remedied, but this question still remains valid.


I am an ex-Windows user, I noticed that minimum level of screen brightness on ubuntu is way brighter than minimum level on windows when I was using it on the same hardware. I was wondering if I can set the brightness level on ubuntu at a level even lower than the minimum level it allows, because default minimum brightness on ubuntu is too brighter for me. Is there any tweak with system settings which I can employ to reduce my screen brightness even further than what default system settings allow?

I have this laptop that doesn't handle the backlight very well.  In /etc/default/grub, I have added a acpi_backlight=vendor function to get it to work at all. Which is cool, and the backlight now actually works, but the minimum backlight setting is still pretty high.  Is there any way to decrease the backlight below minimum? I don't mind having to type in the terminal to do that, as I won't need to do it often (just at night etc.)


I want to use a rigidbody AddForce() method on an object to launch it over from the enemy to the player, like throwing a ball at a target. The problem is, I'm not sure how much force is required to use in the AddForce() method and it is taking too long to figure it out, and adding to that, the force would be different if I was farther away. I found this helpful guide but it is not in 3D: . Could someone explain step by step in an easy to understand manner how to calculate the force required to get an object launched perfectly onto a target? (I'm not very good at math, haha...) Here's some images from that thread that will help illustrate the desired result:

I am trying to launch an object at a target, given its position, its target position, the launch speed, and the gravity.  I am following this formula from :  $$ \theta = arctan \bigg( \frac{v^2 \pm \sqrt{v^4-g(gx^2 + 2yv^2)}}{gx} \bigg) $$  I have simplified the code to the best of my ability, but I still cannot consistently hit the target.  I am only considering the taller trajectory, of the two available from the +- choice in the formula.  Does anyone know what I am doing wrong?  using UnityEngine;  public class Launcher : MonoBehaviour {     public float speed = 10.0f;      void Start()     {         Launch(GameObject.Find("Target").transform);     }      public void Launch(Transform target)     {         float angle = GetAngle(transform.position, target.position, speed, -Physics2D.gravity.y);         var forceToAdd = new Vector2(Mathf.Cos(angle), Mathf.Sin(angle)) * speed;         GetComponent<Rigidbody2D>().AddForce(forceToAdd, ForceMode2D.Impulse);     }      private float GetAngle(Vector2 origin, Vector2 destination, float speed, float gravity)     {         float angle = 0.0f;          //Labeling variables to match formula         float x = Mathf.Abs(destination.x - origin.x);         float y = Mathf.Abs(destination.y - origin.y);         float v = speed;         float g = gravity;          //Formula seen above         float valueToBeSquareRooted = Mathf.Pow(v, 4) - g * (g * Mathf.Pow(x, 2) + 2 * y * Mathf.Pow(v, 2));         if (valueToBeSquareRooted >= 0)         {             angle = Mathf.Atan((Mathf.Pow(v, 2) + Mathf.Sqrt(valueToBeSquareRooted)) / g * x);         }         else         {             //Destination is out of range         }          return angle;     } }


I have this error message. [ 0.367803 ] Initramfs unpacking failed: Decoding failed /dev/sda5: recovering journal /dev/sda5: clean, 318502/6111232 f1les, 3573298/24413696 blocks You are in emergency mode. After logging in type "journalctl -xb" to view system logs, "systemctl reboot" to reboot, "systemctl default" or "exit" to boot into default mode. Press Enter for maintenance. (or press Control-D to continue) Reloading system manager configuration Starting default target

On bootup, filesystem check occurs and it stops at 61% and I am redirected to a page with the message you are in the emergency mode. I don't know what to do next.  This is the message that I get at the screen   You are in emergency mode. After logging in, type .......  Press Enter for maintenance (Or press ctrl+D to continue):   But when I press Ctrl+D it again directs me back to the same screen.


I know it is possible to protect file from printing with Adobe tools, but is this done on latex layer or with pdf tools? And is it also possible to protect created pdf file with password in following situation: I have latex document, that is intended for customer (as pdf) and I am afraid customer will not pay me for this document. What I want is that the customer will be able to open and review file only first time, and then the pdf locks with password I've preset. Is this possible?

My questions is very simple. How can I set security setting for a PDF file created with PDFLatex?  I should set some password or print permissions, etc.


See  for a related question.  Let $X$ be a space that satisfies the hypotheses used to construct a universal cover $\overline{X}$. Let $\pi = \pi_1(X)$ and consider the action of the group $\pi$ on the space $\overline{X}$ given by the isomorphism of $\pi$ with $\text{Aut}(\overline{X})$. Let $A$ be an abelian group and let $\mathbb{Z}[\pi]$ act trivially on $A$, $a \cdot \sigma = a$ for $\sigma \in \pi$ and $a \in A$.  How do I see that the action of $\pi$ on $\overline{X}$ induces an action of $\mathbb{Z}[\pi]$ on the singular chain complex $C_*(\overline{X})$ such that each $C_q(\overline{X})$ is a free $\mathbb{Z}[\pi]$-module and$$C_*(X; A) \cong A \otimes_{\mathbb{Z}[\pi]} C_*(\overline{X})?$$

Let $X$ be a space that satisfies the hypotheses used to construct a universal cover $\overline{X}$. Let $\pi = \pi_1(X)$ and consider the action of the group $\pi$ on the space $\overline{X}$ given by the isomorphism of $\pi$ with $\text{Aut}(\overline{X})$. Let $A$ be an abelian group and let $\mathbb{Z}[\pi]$ act trivially on $A$, $a \cdot \sigma = a$ for $\sigma \in \pi$ and $a \in A$.  Now, assume that $X$ is a CW complex. How do I see that $\overline{X}$ is a CW complex such that the action of $\pi$ on $\overline{X}$ induces an action of the group ring $\mathbb{Z}[\pi]$ on the cellular chain complex $C_*(\overline{X})$ such that each $C_q(\overline{X})$ is a free $\mathbb{Z}[\pi]$-module and$$C_*(X; A) \cong A \otimes_{\mathbb{Z}[\pi]} C_*(\overline{X})?$$


Question : Suppose the quadratic polynomial $p(x)=ax^2 + bx + c~$ has positive coefficients $a, b, c$ in arithmetic progression in that order.If $p(x)=0$ has integer roots $\alpha$ and $\beta$, then what is the value of $\alpha + \beta + \alpha \beta$ ?   My attempt: I am not aware of any inequality of some sort if it exists, but I could not get far by trying substitutions over these unknown variables.

The terms $a,b,c$ of quadratic equation $ax^{2}+bx+c=0$ are in A.P. and positive. Let this equation have integral root $\alpha,\ \beta$. Then find the value of $\alpha+ \beta + \alpha \cdot \beta$ ?   please point where I'm wrong:  Let common difference be $d$  $\implies \alpha+ \beta + \alpha \cdot \beta=\dfrac{c-b}{a}=\dfrac{d}{a} \implies a|d \ \ \ \ \longrightarrow  \ \ \ \ \              \because (b=a+d$, $c=a+2d)$  Also , $ax^{2}+(a+d)x+(a+2d)=0$.   $\implies$ $\alpha,\ \beta=\dfrac{-(a+d) \pm \sqrt{(a+d)^{2}-4\cdot a \cdot (a+2d)}}{2a}$.   For this to be integer $\sqrt{(a+d)^{2}-4\cdot a \cdot (a+2d)}$ must be perfect square.  $\implies$ ${(a+d)^{2}-4\cdot a \cdot (a+2d)}=p^{2}$ for some $p$.  $\implies -3a^{2}+d^{2}-6ad=p^{2}$  $\implies -3a^{2}+a^{2}q^{2}-6a^{2}q=p^{2}$ $\because$ $a|d \implies aq=d$ for some $q$.  $\implies a^{2}(-3+q^{2}-6q)=p^{2}$   $\implies -3+q^{2}-6q\ $  has to be perfect square. By trial $q=7$  But I need to get this without trial, please help.


Someone asked me this - I think the answer is no for a number of reasons, but I wanted to confirm. Is there any way to open an iPad app on a mac desktop or laptop?  For example I download a publisher's ipad reader - call it the WSJ's, for example - could I run it on my iMac and buy issues etc?

I need to install .ipa file to my iPhone simulator.   I tried to change the extension .ipa to .zip and extracted it.  And I got the Payload folder and moved the application inside to my iPhone simulators applications folder found at: /Library/Application\ Support/iPhone Simulator/6.1/Applications/.   Application appears on iPhone Simulator, But the application did't running. How to solve the problem then how to run the app.


I am new to blender and have a question on how to import a stl file and then edit it's wireframe so that it can be laser engraved on acrylic. Similar to to photo below, how can I adjust x,y,z axis wires as needed?  Thanks all

I am trying to reproduce on my CNC a wireframe skull that was etched on acrylic and put into an LED base. It is made by a company called Bulbing; I found it on Youtube. I was hoping that some one might be able help me with this project. Useful  about these lamps.    -from .  Edit: To clarify what the original asker is looking for, How do you take a 3d model and give it a wireframe appearance then output it as a 2d image (preferably vector)?  The objects in the picture are flat pieces of clear acrylic with LEDs at the bottom.  The light reflects off the engraved areas, and if a 2d view of a 3d wireframe is engraved it has the 3d effect shown in the image.


I am citing a book, and I would like to reference a specific theorem within that book. Usually, I would use something like      \cite[Theorem~4]{Reference}   which would have produced something like [1, Theorem 4] as an output. However I am using the memoir document class, and when I try to do that I get the following error:      ! Argument of \@citex has an extra }.   Is there any way to circumvent this without too much pain?  (Removing the [Theorem~4] part from the code works just fine.)

When I try to cite a book in such a way  \begin{theorem}[\cite[p.~90]{bibitem}] Theorem body. \end{theorem}   I've got an error because of multiple use of [ and ]. Is it possible to cite in such a way in theorem argument? Would be great if it could be done without redefine of \cite command.


Given $0 < \varepsilon < \frac{1}{10}$, does there exist a measurable subset $E \subset \mathbb{R^1}$ such that $\varepsilon < \frac{|E\cap{I}|}{I} < 1-\varepsilon$ for every finite interval I =[a,b]? Prove or disprove it . Here ||denotes the Lebesgue measure.  I think it is exist . But I have no ideal of the example.

This question is exercise 4.10 of Richard F. Bass's Real Analysis for Graduate Students, 2nd edition.  Let $\epsilon \in (0,1)$, let $m$ be Lebesgue measure, and suppose $A$ is Borel Measurable subset of $\mathbb R$. Prove that if $$ m(A\cap I)\leq (1-\epsilon)m(I)$$  for every interval $I$, then $m(A)=0$.  Collection of my thoughts  1. Try to prove by contradiction, suppose $m(A)=a>0$ Borel Measurable Set satisfies the condition given. A property of any Borel Measurable Set on $\mathbb R$ is $A$ contains a closed set $F$ and is contained in open set $O$, and the measure of $F$ and $O$ can be arbitrarily close to $a$. 2. Obviously $A$ contains no interval, but it does not lead to contradiction, because we can find an example of $m(A)>0$ that contains no interval(fat Cantor Set(remove middle 1/4 each time) has measure $1/2$ and contains no interval).  2'. For fat Cantor Set $C$ and given $\epsilon>0$ how could we construct an interval I satisfies $m(C \cap I)>(1-\epsilon)m(I) ?$   Maybe try to write Borel measurable set as countable union/intersection of intervals.   I'm stucked here and will appreciate any help, some examples/special case will be great too.


I have a simple script that stores the user info in a file and then locks the screen:  #!/bin/bash echo $USER > /tmp/file.txt # Lock the screen: gnome-screensaver-command -l   When I execute it from the terminal, my username is stored inside. But when it is executed from the shortcut Super+L, it just locks the screen, and there is no file present. Why is this?

I want to change the key bindings on some of the keys on my keyboard.  I want some to run commands and others to activate different keys.  What applications can I use to do this?      Index:       (from within System Settings)             I'm still looking for answers using dconf and any other method.


I'm looking for something to provide faster X11 fowarding than ssh -X provides. I do not need a full GUI session or the ability to drop/resume user sessions. I use NX regularly, but as far as I can tell, there's no way to use it without a virtual desktop where all the graphics get painted. (See: ) VNC also seems to work only with a virtual desktop; same with X2Go.  What I want is something I can run from a terminal that will only open a graphics window and draw to it when it needs to (like ssh -X does). Does this exist? Maybe I've just missed the proper way to do it in something like NX. I've done a ton of searching--I look into this every couple months without a solution--but maybe I'm just searching for the wrong thing.  (Full use case: I'm running Sublime Text on a Linux desktop, and I connect to R running on a remote Linux server via SublimeREPL, which is more or less a terminal emulator within Sublime Text. Plotting things from R happens in a forwarded X window, and it's extremely slow using ssh -XC. I'd love to be able to send the terminal+graphics connection over NX, but NX doesn't seem to support single applications like this; it forces a full-blown user session with a virtual desktop.)

I try to launch Firefox over SSH, using  ssh -X user@hostname   and then  firefox -no-remote   but it's very very slow.  How can I fix this? Is it a connection problem?


why does this code crash? is using strcat illegal on character pointers?   #include <stdio.h> #include <string.h>  int main() {    char *s1 = "Hello, ";    char *s2 = "world!";    char *s3 = strcat(s1, s2);    printf("%s",s3);    return 0; }   please give a proper way with referring to both array and pointers.

The following code receives seg fault on line 2:  char *str = "string"; str[0] = 'z';  // could be also written as *str = 'z' printf("%s\n", str);   While this works perfectly well:  char str[] = "string"; str[0] = 'z'; printf("%s\n", str);   Tested with MSVC and GCC.


I'm using VM Ware (specifically the player) and i'd like to attach a multiple mouses and have one for each VM (same idea with keyboard but i havent tried keyboards yet). I'd like several people using their own vm. I cant seem to figure out how to lock the mouse into the VM. If i plug in a mouse windows uses both of them and i need to click onto an instance of vmware to get the mouse working there.  I tried clicking the USB area at the bottom of the player window and i got the error message     Cannot connect "BRAND USB Optical Mouse" to this virtual machine. The host requires this device for input.   Is it possible to dedicate a mouse/keyboard to a VM instance? I'm willing to use another VM software (but preferably free)

Let's say I have a PC with two monitors atached. I'm running e.g. Windows Vista natively, and start up a virtual Ubuntu PC. I change to fullscreen mode so that on one Monitor, I see my Windows Desktop, and on the other one, the Ubuntu Desktop. I can now use my mouse and Keybord for both of them.  This works fine, but I'd really like to connect a second mouse and a second keyboard to my physical PC, and do some configuration so that one set of input devices is used for Windows, and another set for the virtual Ubuntu. Then two persons could work at the same time, as if they were using two separate computers, although there is only one physical machine.  I'm currently using Sun VirtualBox and it has a feature to assign specific USB devices to the virtual machine. While this sometimes works for e.g. external disk drives, it never worked for mice and keyboards for me (yes, of course my input devices are attached via USB!).  I'd like to know a solution that works with VirtualBox, but any answer is appreciated, even if another virtualization software or some additional hardware was needed.


I like the chat feature and I am one of the regular users for it. The thing is, sometimes I love to read what guys talk about in a chat room, but without being visible to them usually to avoid pings  (we have a very good chat community in Travel.SE). Currently I open another browser where I am not logged in and open the chat there to see it without appearing. I also can load the transcript but that requires me to refresh.  Is there a way to be a spectator in a chat room (your name not in the users list) and without being logged out? If not can that be done?  Note: There is a  which suggested the transcript, which is not a practical solution IMO. So I am reviving that request again hoping it will get attention.

E.g.  I know that I can browse the chat when I'm not logged on. But what if I am logged on and want to spare the inconvenience of logging off/multiple browsers?


The JTAG interface is pretty new to me. I know most of nowadays ARM mcu's are programmed via JTAG. However what programming cable is usually used? I found this one, and I've seen some people use it in the past:   But it is not sold anymore. What are other alternatives? Is it sufficient to connect the TCK, TMS, TDI and TDO of the mcu to the TCK, TMS, TDI and TDO of the programming cable, via a boxheader or so, in order to program it or is additional circuitry necessary?  I've heard there is something as SWD as well, but that's only for debugging not programming if I understand it correctly.  I am working with this mcu: cortex M4 TM4C1294NCPDT

I have some hard time understanding JTAG for programming.  I have an mcu that can only be programmed via JTAG.  What are some easy chips to start with in order to program an mcu via JTAG? I suppose I d need a chip (mentionned in the previous sentence) in order to convert the serial data received via usb to the "JTAG-equivalent"?  I am trying to program this mcu: TM4C1294 cortex M4, which can only be programmed via JTAG.  EDIT: a lot of you guys are talking about an FTDI2232 chip. But how would you wire an FTDI chip to the mcu? I mean the ftdi chip does (as far as I know a conversion to TTL and that s it). So you would then have all your data on the TX and RX pins. But with JTAG you need a TDI,TDO, TCK and a TMS pin. So I think you need another chip to do the conversion. No?


I just  on an off-topic post on  with 3 different links. Two of them were magic links. I referred a User to [so], mentioning (and linking) the guidelines (on-topic help). And when I looked at the links, they were almost indistinguishable from the normal text:        And here the same, with all three links marked:        For reference, :visited links have this hex-code: #18529a And normal links have: #4e82c2

(This is mainly for Stack Overflow, I did personally not check out color schemes on the other sites. But a  has been raised for beta sites.)  I don't think the current style for visited links on Stack Overflow posts is very nice. The text is black and links are #4A6B82 which looks almost like black or a very dark grey on my screen. That's not very accessible (and that's in spite of my good eyesight).  Additionally, links in inline code sections do not get underlined on hover, which makes them even harder to spot. Sometimes I link to documentation by putting a link on (<- like this), and it is very hard to notice that it is even there (apparently, Meta has the same problem…).  I would find brighter links and consistent underlining very helpful.  I'll tag this as [bug] because I think link coloring is actually broken. And the other choices ([feature-request] [discussion] [support]) don't really fit.


How do I limit the maximum number of authors displayed in the references.  Example:  @ARTICLE{2013Natur.495...76P,    author = {{Pietrzy{\'n}ski}, G. and {Graczyk}, D. and {Gieren}, W. and     {Thompson}, I.~B. and {Pilecki}, B. and {Udalski}, A. and {Soszy{\'n}ski}, I. and   {Koz{\l}owski}, S. and {Konorski}, P. and {Suchomska}, K. and   {Bono}, G. and {Moroni}, P.~G.~P. and {Villanova}, S. and {Nardetto}, N. and    {Bresolin}, F. and {Kudritzki}, R.~P. and {Storm}, J. and {Gallenne}, A. and    {Smolec}, R. and {Minniti}, D. and {Kubiak}, M. and {Szyma{\'n}ski}, M.~K. and      {Poleski}, R. and {Wyrzykowski}, {\L}. and {Ulaczyk}, K. and    {Pietrukowicz}, P. and {G{\'o}rski}, M. and {Karczmarek}, P.    },         title = "{An eclipsing-binary distance to the Large Magellanic Cloud accurate to two per cent}",            journal = {\nat}, archivePrefix = "arXiv",             eprint = {1303.2063},           primaryClass = "astro-ph.GA",         year = 2013,         month = mar,    volume = 495,         pages = {76-79},         doi = {10.1038/nature11878},         adsurl = {http://adsabs.harvard.edu/abs/2013Natur.495...76P},          adsnote = {Provided by the SAO/NASA Astrophysics Data System}   Instead all of the authors showing up I would like to have something like:  G. Pietrzynski, et al., An eclipsing-binary distance to the Large Magellanic Cloud accurate to two per cent. Nature, 495:76–79, Mar. 2013. doi: 10.1038/nature11878.   Many thanks!

I have several entries in my list of references that include of the order of 40 authors. Is there a way to make bibtex automatically reduce these lists to e.g. the first name + "et al."?  I don't want to edit the BibTeX entries manually and I cannot use biblatex. If at all possible I would also make as little changes as possible to the bibliography style.  There are similar questions, but none of those had a concise answer:       natbib e.g. seems to change only the reference within the text, but not the entry in the bibliography.  EDIT: I am using \bibliographystyle{unsrt} as style definition.


I installed Ubuntu in my SSD with my desktop and It worked well. Then I put it on my laptop and I got the error system is running in low-graphics mode. The error prompt before I reach the Ubuntu login screen.  My Ubuntu version is 18.04 LTS and my laptop is a Lenovo T470 with an Intel GPU.  I know that this question was asked a lot, but I tried all the answers I saw. Does anyone have a more up-to-date solution and/or related to Intel graphics drivers? The recovery menu failsafeX didn't work either.  Thanks.

Note: This is an attempt to create a canonical question that covers all instances of "low-graphics mode" error that occurs to a user, including but not limited to installation of wrong drivers, incorrect or invalid lightdm greeters, low disk space, incorrect installation of graphics card like ATI and Nvidia, incorrect configuration of xorg.conf file while setting up multiple monitors among others. If you are experiencing the "low-graphics mode" error when trying to login but none of the following answers work for you, please do ask a new question and then update the answers of this canonical question as and when your new question gets answered.   When I try to boot into my computer, I am getting this error:  The system is running in low-graphics mode Your screen, graphics cards, and input device settings could not be detected correctly. You will need to configure these yourself.   How do I fix the failsafe X mode and login into my computer?  Answer index:


Let $K$ be an algebraic number field. Prove that $O_K$ (collection of integral elements) contains infinitely many prime ideals.  Now this is Dedekind domain. Now what should be the next step?

Given an algebraic number field $K/\mathbb Q$, let $R = \mathbb Z_K$ be the ring the algebraic integers of that fields. Is it possible to say how many prime ideals there are in $R$? I suspect we always have infinitely many, as this is certainly the case for $K=\mathbb Q$ (because then $R = \mathbb Z$).   I was already able to show that an Ideal $I\subseteq \mathbb R$ ($I\neq0$) is prime if and only if it is maximal. One idea would have been showing that you can generate infinitely many fields via $R/I$ but I was never able to show what $R/I$ would be isomorphic to, as I do not really know what the prime ideals $I$ look like.   So have no idea how to go from there, and I'd be happy for every hint!


I will be travelling to Phoenix, USA via London with valid US Visa and onwards journey boarding pass with Indian Passport. I have 18+ hours layover in London. I want to know How likely is to get the 24 hours transit in London. Its a long time and I don't want just to waste it by staying at airport. I want to go to hotel to have some rest and then probably visit some places.  I can see I come under "Transit without Visa concession" but I heard it depends on visa officer to allow to go out or deny. If they won't allow Will I get visa on arrival.   Also I tried to apply for Transit Visa. Its asking me Whether you want to go for sight seeing or not. I said Yes. Its saying me you have to apply for different visa. If I am going out of airport then its natural I will go for sightseeing? I just can't close my eyes and roam around. What other reasons would be there to go out? What do you guys suggest? What to do? I am totally confused.  For those of you who are saying its already answered before. Please read question carefully. Here I am trying to get the exact meaning of Visitor in Transit Visa. That's never answered here in this community.

Is there a website or some other way to find out if I need a transit visa for a short stop in the UK on my way somewhere else? Ideally this should give me the answer for all nationalities, and take into account any other visas I may have.


How can I solve the linear congruence $7x+3 \equiv 4x+1 \pmod{10}$?     I got:  $7x+3 \equiv 4x+1 \pmod {10} :\iff 10\mid (3x+2) \implies \exists k\in \mathbb{Z} : 10k-3x=2$  I want to apply Bézout's identity to find $x$, but therefore I have to get rid of the $2$ and instead have a $1$. Can I just divide by $2$?

When I am faced with a simple linear congruence such as  $$9x \equiv 7 \pmod{13}$$ and I am working without any calculating aid handy, I tend to do something like the following:  "Notice" that adding $13$ on the right and subtracting $13x$ on the left gives: $$-4x \equiv 20 \pmod{13}$$  so that $$x \equiv -5 \equiv 8 \pmod{13}.$$  Clearly this process works and is easy to justify (apart from not having an algorithm for "noticing"), but my question is this: I have a vague recollection of reading somewhere this sort of process was the preferred method of C. F. Gauss, but I cannot find any evidence for this now, so does anyone know anything about this, or could provide a reference? (Or have I just imagined it all?)  I would also be interested to hear if anyone else does anything similar.


I am very new to QGIS for the primary purpose of creating a slopes layer so we know where slopes are above 15% or 20% or whatever we finally decide.  I have used our DEM to create a slope geotif and have used that to try and create a classified layer, but that is where my problems seem to begin. I used this formula to create my classified layer ((slope@1 < 15) OR (slope@1 > 60)) = 0 and while I get a new layer I am not able to view it, no matter how I manipulate the properites. I also tried to follow the  for the display that says to do this:      9.4.16. Setting the style for the reclassified layers         Open the Style tab in the layer’s Properties dialog as usual.   Under the heading Load min / max values from band, select the Actual    (slower) radio button.   Click the Load button.         The Custom min / max values fields should now populate with 0 and 1,   respectively. (If they do not, then there was a mistake with your   reclassification of the data, and you will need to go over that part   again.)         Under the heading Contrast enhancement, set the Current dropdown list    to Stretch To MinMax.   Click OK.      I do not come up with the 0 and 1 that the instructions speak of (I am not using their tutorial data) but it seems that I should be able to see the layer.

I'm using QGIS. I want a raster layer with 6 different colors each color representing a certain value range (e.g. -1 to 0 red, 0 to 0.2 orange).  In the layer style menu I can only approximate colors.


I have a db file in asset folder how can I use it. I must be able to read and write the database file  If I use      SqliteDatabase.open(context.openassest().open(filrname),null);   Exception db file not found    Don't check. The syntax I have done correctly in my lap see the content

If your application requires a database and it comes with built in data, what is the best way to ship that application? Should I:   Precreate the SQLite database and include it in the .apk? Include the SQL commands with the application and have it create the database and insert the data on first use?   The drawbacks I see are:   Possible SQLite version mismatches might cause problems and I currently don't know where the database should go and how to access it. It may take a really long time to create and populate the database on the device.   Any suggestions? Pointers to the documentation regarding any issues would be greatly appreciated.


I was looking for a simple way to round a double value to 10 digits but I didn't found even one way that look good to me, everything was too complicated.  I hope someone could help me, for example: the value 0.83426945721236485 will become 0.8342694572  Thank you in advance.

What I would like is a method to convert a double to a string which rounds using the half-up method - i.e. if the decimal to be rounded is 5, it always rounds up to the next number. This is the standard method of rounding most people expect in most situations.  I also would like only significant digits to be displayed - i.e. there should not be any trailing zeroes.  I know one method of doing this is to use the String.format method:  String.format("%.5g%n", 0.912385);   returns:  0.91239   which is great, however it always displays numbers with 5 decimal places even if they are not significant:   String.format("%.5g%n", 0.912300);   returns:  0.91230   Another method is to use the DecimalFormatter:  DecimalFormat df = new DecimalFormat("#.#####"); df.format(0.912385);   returns:  0.91238   However as you can see this uses half-even rounding. That is it will round down if the previous digit is even. What I'd like is this:  0.912385 -> 0.91239 0.912300 -> 0.9123   What is the best way to achieve this in Java?


Sometimes, links point to sites which are dead, or not what they used to be, thus are broken.  Sometimes, those sites do have mirrors.  Is it possible to update all broken links in the various comments, questions and/or answers massively, to change to the still working mirror?

There are many links posted in answers, and some in questions, that are either stale or broken.  An example is the change to  on-line documentation this year to do away with separate 'Optional' and 'Core' tasks areas in the documentation - the old links 404 now.  I've fixed a bunch of 'optionaltasks' broken links, but searching for 'coretasks' in Stack Overflow questions returns over 300 matches...  Are there any tools for us to review and fix these - with an emphasis on the fixing - without sifting through completely manually?  Is it time for some refactoring tools for Stack Overflow content, in particular, for links?  Also, I'd be interested to know if there is an analysis of links (as found in the Stack Overflow data dumps) out there. Answer: there is a  of a sample of links and images, but it's getting a bit out-of-date.


Upon reading the 5e Player's Handbook, I've noticed that the level cap seems to stop at a hard 20, which, too me, is too small. I've also read the Dungeon Master's Guide and found the Epic Boons system, but those all seem extremely under powered or over powered compared to one another. I've looked, to no avail, for an official system for playing past lvl 20, or at least an appealing homebrew one, but, as I said before, I have yet to find one.

Level 20 is shown to be the level cap. So does getting 30000 XP for the epic boons or added ability scores implement into character's statistics such as max prepared spells or max health increase?   For example a 20th level Wizard with 20 intelligence can prepare a maximum of 25 spells.  After gaining 30000 XP would that wizard be considered level 21 and get 26 maximum spells?


I know the hardy Weinberg equation but that is for the amount of alleles not the amount of phenotypes. So if there are 600 black(dominant) organisms in the population and 400 green(recessive) organisms. Can you figure out how many of the blacks are actually heterozygous?

I really fail to understand Hardy-Weinberg equilibrium and can't find an easy enough source of information.  Can you help me to understand Hardy-Weinberg equilibrium?  My goal is to be able to solve the following kind of problem     In a population with two alleles for a certain locus, B and b, the allele frequency of B is 0.7. What is the frequency of heterozygotes if the population is in Hardy-Weinberg equilibrium?


We are migrating to Lightning and we are replacing URL based 'List Button' on Opportunity related list under Accounts. We want to pre-default standard 'Opportunity Name' field with 'Account Name' value. SF suggests 'Quick Actions' which cannot be mapped on Opportunity related list. Is there any other way to fix this?

I have action override on New Case button which runs our custom component.  As you know, we can create a new Case from different places in org, e.g. from related lists. When creating a Case from related list on Account using standard action in Lightning we have prepopulated AccountId to the lookup field. Is it possible to do the same with custom component? I can't catch the AccountId using force:hasRecordId, because action override redirects me to the new page with custom component where I don't have a context of Account. URL also doesn't contain its Id. What can I do to grab Id of context object and populate it to my component?


There was "" pdf in the 2016 playtest material. A Beastmaster Ranger was considered the weakest class by many GMs and players, which apparently caused the need for a "revised" version. However, I've never heard how exactly the playtesting ended. Googling "ranger revised" gives me the same 2016 pdf and nothing more. What happened to the "revised" ranger from the Unearthed Arcana? Was it renamed from "revised" to something else? Was it published in any official source book, changed or unchanged? (I don't have access to all of them so I can't check it myself for now) Or was it abandoned by WoTC? This is a technical duplicate of , which was answered in 2017, but things probably changed in 2021, so that accepted answer doesn't answer the question anymore. Also, I'm asking about Beastmaster Ranger specifically, which could be changed/revised in latter source books (XGtE,TCoE, whatever) as an additional Ranger archetype.

14 months ago, an  supplement was published that discussed how the ranger described in the Player's Handbook was under powered. These rules reimagined the ranger's abilities, and suggested that an official version would be released later.     Finally, we come to implementation. If this iteration of the ranger, or a future revision of it, grades high enough, our plan is to present it as a revised ranger in a future D&D sourcebook.   Does that Sourcebook exist yet? If not, have the devs given an update or told us their intentions?


I have the series $\sum_{n=0}^\infty \frac{n}{2^n}$. I must show that it converges to 2.   I was given a hint to take the derivative of $\sum_{n=0}^\infty x^n$ and multiply by $x$ , which gives   $\sum_{n=1}^\infty nx^n$ , or $\sum_{n=0}^\infty nx^n$.   Clearly if I take $x=\frac{1}{2}$ , the series is  $\sum_{n=0}^\infty \frac{n}{2^n}$. How do I proceed from here?

This problem comes from another equation on another question (. I tried to split it in half but I found out that $$\sum_{k=0}^\infty \frac{k}{2^k}$$ can't be divided. Knowing that $$\sum_{k=0}^\infty x^k=\frac{1}{1-x}$$ I wrote that $$\sum_{k=0}^\infty \frac{k}{2^k}=\sum_{k=0}^\infty \left(\frac{\sqrt[k] k}{2}\right)^k=\frac{1}{1-\frac{\sqrt k}{2}}=\frac{2}{2-\sqrt[k] k}$$ But that's not what I wanted. Could anyone help me?


I'm trying to align li items from the top so that they look like this:    However, with my current code, I'm unsure why my list is coming out like so...    .customer-experience .list-items {   padding-top: 110px;   box-sizing: border-box;   list-style: none; }  .customer-experience .list-items li {   width: 33%;   float: left; }  .customer-experience .list-items li h3 {   font-size: 90px;   color: #333333;   font-family: "Oswald";   font-weight: 400;   margin-bottom: 0;   padding-bottom: 50px;   border: 1px solid red; }  .customer-experience .list-items li p {   color: #333333;   font-weight: 400;   font-size: 1.875rem; }

64%

Customers want personalised offers

Up to

€20 million

Fine for GDPR non-compliance

52%

Customers say not enough is done to make them feel welcome

     I've tried to add a fixed height, but 1. I don't want to add fixed heights, 2. It doesn't work anyway. The second list item also has a
 above it, which is maybe contributing to the issue? Ideas?

I have a div with two images and an h1. All of them need to be vertically aligned within the div, next to each other. One of the images needs to be absolute positioned within the div. What is the CSS needed for this to work on all common browsers?

testing...


I feel like I have tried everything, but I also have no idea what I'm doing, so I hope you guys can help me out. I have installed Ubuntu Restricted Extras from the Software center. Shockwave Flash 11.2 r202 is listed in the Firefox Plugins, but flash does not work in my browser. I'm using Ubuntu 14.04.  Ive tried running:  sudo apt-add-repository “deb http://archive.canonical.com/ $(lsb_release -sc) partner”   in terminal, but it returns   Error: need a single repository as argument   I'm a complete noob to any of this, so help is much appreciated.  Thank you.

I have had significant problems with watching flash video in 64-bit Ubuntu.  Does anyone know of a good way to get flash running on the platform?


I have an issue with getting correct date of last Monday of previous month. I think there isn't absolutely right to calculate it like in  question and want to refuse arithmetic operations with constants. This code working as expected:  public class mCalendar {   private int thisMonth;   private int prevMonth;   private int lstDayThisMonth;   private int lstDayPrevMonth;   private int weekOffset;   private int LstMnd;   public String monthLetter;   Locale locale = Locale.getDefault();   private Calendar mCal;  public mCalendar(){   this.mCal = Calendar.getInstance();   mCal.set(Calendar.MONTH,0);   this.thisMonth = mCal.get(Calendar.MONTH);   this.prevMonth = thisMonth - 1;   this.lstDayThisMonth = mCal.getActualMaximum(Calendar.DAY_OF_MONTH);   this.monthLetter = mCal.getDisplayName(Calendar.MONTH, Calendar.LONG, locale);    mCal.set(Calendar.MONTH,prevMonth);   this.lstDayPrevMonth = mCal.getActualMaximum(Calendar.DAY_OF_MONTH);   mCal.set(Calendar.DAY_OF_MONTH,lstDayPrevMonth);   this.LstMnd = mCal.get(Calendar.DAY_OF_WEEK_IN_MONTH);   mCal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);   mCal.set(Calendar.DAY_OF_WEEK_IN_MONTH, LstMnd);   this.weekOffset = mCal.get(Calendar.DAY_OF_MONTH); }   But when I set Calendar.MONTH to 1 in second instruction of constructor's body Calendar.DAY_OF_MONTH return frist Monday of February. I expect the function return me January 26 but it's return February 2. I think it's happens because February 1 it's a Sunday but, for example, for March code is working correct.  Help me please, i'm confused)

I am working on a project where the requirement is to have a date calculated as being the last Friday of a given month.  I think I have a solution that only uses standard Java, but I was wondering if anyone knew of anything more concise or efficient. Below is what I tested with for this year:      for (int month = 0; month < 13; month++) {         GregorianCalendar d = new GregorianCalendar();         d.set(d.MONTH, month);         System.out.println("Last Week of Month in " + d.getDisplayName(d.MONTH, Calendar.LONG, Locale.ENGLISH) + ": " + d.getLeastMaximum(d.WEEK_OF_MONTH));         d.set(d.DAY_OF_WEEK, d.FRIDAY);         d.set(d.WEEK_OF_MONTH, d.getActualMaximum(d.WEEK_OF_MONTH));         while (d.get(d.MONTH) > month || d.get(d.MONTH) < month) {             d.add(d.WEEK_OF_MONTH, -1);         }         Date dt = d.getTime();         System.out.println("Last Friday of Last Week in  " + d.getDisplayName(d.MONTH, Calendar.LONG, Locale.ENGLISH) + ": " + dt.toString());     }


I have some big problems with my packages in my Ubuntu 16.04 Xenial. In the last few days I've changed my sources.list a lot and I've added some bunches of PPAs. Now I'm lost and don't know what to do.  I think I'm an intermediate Linux user. I started to use Debian 2 or 3 years ago, but I have problems everyday. In some months I had to format my machine more than 3 times due to problems with packages, drivers and multi-architecture.  This problem started when I tried to install VLC media player. They showed me that I have dependencies with libgles1-mesa and the system can't solve by itself. Then it asked me to try apt-get -f install to force the installation of dependencies, but my system can't solve this again.  After a lot of changes and attempts, I couldn't solve my problem, so here is some information about my status. I hope someone can help me to fix this.  I'm sorry about this, but my system is in Brazilian Portuguese. [Edit: the below is partially translated.]  uname -a  Linux Max-Notebook 4.8.0-45-generic #48~16.04.1-Ubuntu SMP Fri Mar 24 12:46:56 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux   sudo apt-get install vlc  Reading package lists... Done Building dependency tree Reading state information... Done You might want to run 'apt-get -f install' to correct these: The following packages have unmet dependencies:  libgl1-mesa-glx : Depends: libglapi-mesa (= 17.0.1+git20170319+17.0.07adc57f-0ubuntu0ricotz~xenial) but 11.2.0-1ubuntu2 is to be installed  libglapi-mesa : Breaks: libglapi-mesa:i386 (!= 11.2.0-1ubuntu2) mas 17.0.1+git20170319+17.0.07adc57f-0ubuntu0ricotz~xenial está para ser instalado  libglapi-mesa:i386 : Quebra: libglapi-mesa (!= 17.0.1+git20170319+17.0.07adc57f-0ubuntu0ricotz~xenial) mas 11.2.0-1ubuntu2 está para ser instalado  libgles2-mesa : Depende: libglapi-mesa (= 17.0.1+git20170319+17.0.07adc57f-0ubuntu0ricotz~xenial) mas 11.2.0-1ubuntu2 está para ser instalado  vlc : Depende: vlc-nox (= 2.2.2-5ubuntu0.16.04.1) but will not be installed        Depende: libgles1-mesa (>= 7.8.1) mas não será instalado ou                 libgles1        Depende: libsdl-image1.2 (>= 1.2.10) mas não será instalado        Depende: libva-drm1 (>= 1.1.0) mas não será instalado        Depende: libva-x11-1 (>= 1.0.3) mas não será instalado        Depende: libvlccore8 (>= 2.2.0) mas não será instalado        Recommends: vlc-plugin-notify (= 2.2.2-5ubuntu0.16.04.1) mas não será instalado        Recomenda: vlc-plugin-samba (= 2.2.2-5ubuntu0.16.04.1) mas não será instalado E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).   sudo apt-get -f install  Lendo listas de pacotes... Pronto Construindo árvore de dependências        Lendo informação de estado... Pronto Correcting dependencies... failed. Os pacotes a seguir têm dependências desencontradas:  libgl1-mesa-glx : Depende: libglapi-mesa (= 17.0.1+git20170319+17.0.07adc57f-0ubuntu0ricotz~xenial) mas 11.2.0-1ubuntu2 está instalado  libglapi-mesa : Quebra: libglapi-mesa:i386 (!= 11.2.0-1ubuntu2) mas 17.0.1+git20170319+17.0.07adc57f-0ubuntu0ricotz~xenial está instalado  libglapi-mesa:i386 : Quebra: libglapi-mesa (!= 17.0.1+git20170319+17.0.07adc57f-0ubuntu0ricotz~xenial) mas 11.2.0-1ubuntu2 está instalado  libgles2-mesa : Depende: libglapi-mesa (= 17.0.1+git20170319+17.0.07adc57f-0ubuntu0ricotz~xenial) mas 11.2.0-1ubuntu2 está instalado E: Erro, pkgProblemResolver::Resolve gerou falhas, isto pode ser causado por pacotes mantidos (hold). E: Impossível corrigir dependências   cat /etc/apt/sources.list  deb http://security.ubuntu.com/ubuntu/ xenial-security main universe restricted deb http://br.archive.ubuntu.com/ubuntu/ xenial-updates main universe restricted deb http://br.archive.ubuntu.com/ubuntu/ xenial main universe restricted   If you need any information just ask me.  I can't format my notebook because I'll have a lot of problems again to install and configure Android Studio, Java, Netbeans, Vagrant, Composer, Git, VirtualBox, Astah, and a lot of other softwares.  Thanks guys!

Occasionally, when I'm installing stuff, I get an error like the following:  Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation:  The following packages have unmet dependencies:  package1 : Depends: package2 (>= 1.8) but 1.7.5-1ubuntu1 is to be installed E: Unable to correct problems, you have held broken packages.   How can I resolve this?


when i try to remove element there is an error, i have uploaded the error in the image section. any help to fix? of any other way to get the code fixed and working smoothly and it it works while deleting the middle element not the first or second duplication issue ,fixed using iterator. hatsooff to stack overflow . all good  import java.util.*;  public class EarthquakeList { private ArrayList<EarthquakeNode> records;  public EarthquakeList() {    records = new ArrayList<EarthquakeNode>();  }  public boolean isempty() {       return true; }   public void add(String EarthquakeLo,String EarthquakeDt, double EarthquakeSgth, int EarthquakeDu) {    EarthquakeNode en = new EarthquakeNode(EarthquakeLo, EarthquakeDt, EarthquakeSgth, EarthquakeDu);    records.add(en); }   public boolean remove(String EarthquakeLo,String EarthquakeDt) {    boolean flag= false;    for(EarthquakeNode earthquake: records)    {        if(earthquake.getLocation().equalsIgnoreCase(EarthquakeLo))        {            if(earthquake.getDate().equals(EarthquakeDt))            {                records.remove(earthquake);                flag=true;             }        }    }    return flag;  }    public EarthquakeNode search(String EarthquakeLo,String EarthquakeDt) {    EarthquakeNode node= null;    for(EarthquakeNode earthquake: records)    {        if(earthquake.getLocation().equalsIgnoreCase(EarthquakeLo))        {            if(earthquake.getDate().equals(EarthquakeDt))            {                 node=earthquake;            }        }    }    return node; }   public boolean clear() {     int count=records.size();    for(EarthquakeNode earthquake: records)    {        count=count-1;        records.remove(earthquake);       }    if(count==0)    {    System.out.println("already empty");    return false;}     else     System.out.println("every thing is removed");    return true; }   public boolean isempty(String EarthquakeLo,String EarthquakeDt) {    boolean flag= false;    for(EarthquakeNode earthquake: records)    {        if(earthquake.getLocation().equalsIgnoreCase(EarthquakeLo))        {            if(earthquake.getDate().equals(EarthquakeDt))            {                flag=true;            }        }    }    return flag; }   public void print() {    for(EarthquakeNode earthquake: records)    {        System.out.println( earthquake.getLocation() +" - "               + earthquake.getDate()+ " - "                + earthquake.getStrength() + " on rector scale"+                "-" + earthquake.getDuration() + "mins");    }  }   }

We all know you can't do the following because of ConcurrentModificationException:  for (Object i : l) {     if (condition(i)) {         l.remove(i);     } }   But this apparently works sometimes, but not always. Here's some specific code:  public static void main(String[] args) {     Collection<Integer> l = new ArrayList<>();      for (int i = 0; i < 10; ++i) {         l.add(4);         l.add(5);         l.add(6);     }      for (int i : l) {         if (i == 5) {             l.remove(i);         }     }      System.out.println(l); }   This, of course, results in:  Exception in thread "main" java.util.ConcurrentModificationException   Even though multiple threads aren't doing it. Anyway.  What's the best solution to this problem? How can I remove an item from the collection in a loop without throwing this exception?  I'm also using an arbitrary Collection here, not necessarily an ArrayList, so you can't rely on get.