text: # Thread: Didn't know to do this on test
  
  1. ## Didn't know to do this on test
  
  I didn't know how to do this problem on the test I took today...could someone work this out?
  
  Differentiate:
  
  $\int \frac{1+x^2}{x^3}dx$
  
  2. Originally Posted by c_323_h
  I didn't know how to do this problem on the test I took today...could someone work this out?
  
  Differentiate:
  
  $\int \frac{1+x^2}{x^3}dx$
  $\frac{1+x^2}{x^3}=\frac{1}{x^3}+\frac{x^2}{x^3}=x^ {-3}+x^{-1}$
  ---
  Now I am confused because it say differentiate after integrate. If you really mean that, then it is,
  $\frac{1+x^2}{x^3}$ because the derivative of an integral and the integral of the derivative is the same.
  
  3. Originally Posted by ThePerfectHacker
  $\frac{1+x^2}{x^3}=\frac{1}{x^3}+\frac{x^2}{x^3}=x^ {-3}+x^{-1}$
  ---
  Now I am confused because it say differentiate after integrate. If you really mean that, then it is,
  $\frac{1+x^2}{x^3}$ because the derivative of an integral and the integral of the derivative is the same.
  yes that's what i thought too! but i haven't seen a "trick" question on a test in years so i thought you could really differentiate it. but shouldn't the answer have a constant added at the end? is is the same with a definite integral?
  
  4. Originally Posted by c_323_h
  yes that's what i thought too! but i haven't seen a "trick" question on a test in years so i thought you could really differentiate it. but shouldn't the answer have a constant added at the end? is is the same with a definite integral?
  First off, I don't think there are really "trick" questions on tests. (After doing some teaching myself) I suspect that there are teachers that make mistakes and won't fess up to it. I've had some teachers obviously do that, anyway.
  
  Anyway, to the question. When you do an indefinite integral you need to introduce a constant. When you differentiate this the constant goes away and you are left with just the original integrand. When you do a definite integral the result is a number. So when you differentiate this you get zero.
  
  So the answer to your question, as THP says, will be the original integrand.
  
  -Dan
  
  5. Oops looks like I read the directions wrong. It said to evalute the indefinite integral. Well this is the answer...teacher went over the test today:
  
  $\int\frac{1+x^2}{x^3}dx =$
  $\int\frac{1}{x^3}+\frac{x^2}{x^3}dx =$
  $\int x^{-3} dx+\int\frac{1}{x}dx =$
  
  $\frac{x^{-2}}{-2} + ln|x| + C$
explanation: The document is a forum thread where a user asks for help with a math problem from a test. The problem involves differentiating an integral. The thread includes the initial question, a response from another user providing a solution, and further discussion about the problem. The user who posted the question later provides the correct solution as given by their teacher.
distilabel_metadata.content: Evaluate the user given text extract and determine if it contains a math question and optionally and answer to this question.
  
  Output rules:
  
  1. Briefly describe the document and mention if it contains a question or a question and answer.
  2. Finalize the output with: Label: no-question,question,question-and-answer,multiple-question,multiple-question-and-answer
distilabel_metadata.role: system
distilabel_metadata.content: # Thread: Didn't know to do this on test
  
  1. ## Didn't know to do this on test
  
  I didn't know how to do this problem on the test I took today...could someone work this out?
  
  Differentiate:
  
  $\int \frac{1+x^2}{x^3}dx$
  
  2. Originally Posted by c_323_h
  I didn't know how to do this problem on the test I took today...could someone work this out?
  
  Differentiate:
  
  $\int \frac{1+x^2}{x^3}dx$
  $\frac{1+x^2}{x^3}=\frac{1}{x^3}+\frac{x^2}{x^3}=x^ {-3}+x^{-1}$
  ---
  Now I am confused because it say differentiate after integrate. If you really mean that, then it is,
  $\frac{1+x^2}{x^3}$ because the derivative of an integral and the integral of the derivative is the same.
  
  3. Originally Posted by ThePerfectHacker
  $\frac{1+x^2}{x^3}=\frac{1}{x^3}+\frac{x^2}{x^3}=x^ {-3}+x^{-1}$
  ---
  Now I am confused because it say differentiate after integrate. If you really mean that, then it is,
  $\frac{1+x^2}{x^3}$ because the derivative of an integral and the integral of the derivative is the same.
  yes that's what i thought too! but i haven't seen a "trick" question on a test in years so i thought you could really differentiate it. but shouldn't the answer have a constant added at the end? is is the same with a definite integral?
  
  4. Originally Posted by c_323_h
  yes that's what i thought too! but i haven't seen a "trick" question on a test in years so i thought you could really differentiate it. but shouldn't the answer have a constant added at the end? is is the same with a definite integral?
  First off, I don't think there are really "trick" questions on tests. (After doing some teaching myself) I suspect that there are teachers that make mistakes and won't fess up to it. I've had some teachers obviously do that, anyway.
  
  Anyway, to the question. When you do an indefinite integral you need to introduce a constant. When you differentiate this the constant goes away and you are left with just the original integrand. When you do a definite integral the result is a number. So when you differentiate this you get zero.
  
  So the answer to your question, as THP says, will be the original integrand.
  
  -Dan
  
  5. Oops looks like I read the directions wrong. It said to evalute the indefinite integral. Well this is the answer...teacher went over the test today:
  
  $\int\frac{1+x^2}{x^3}dx =$
  $\int\frac{1}{x^3}+\frac{x^2}{x^3}dx =$
  $\int x^{-3} dx+\int\frac{1}{x}dx =$
  
  $\frac{x^{-2}}{-2} + ln|x| + C$
distilabel_metadata.role: user
distilabel_metadata.raw_output_q_a_detector_0: The document is a forum thread where a user asks for help with a math problem from a test. The problem involves differentiating an integral. The thread includes the initial question, a response from another user providing a solution, and further discussion about the problem. The user who posted the question later provides the correct solution as given by their teacher.
  
  Label: question-and-answer