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Simplify
\[\tan 9^\circ + \cot 9^\circ - \tan 27^\circ - \cot 27^\circ.\] | We know that $\cot 9^\circ = \tan 81^\circ$ and $\cot 27^\circ = \tan 63^\circ,$ so
\[\tan 9^\circ + \cot 9^\circ - \tan 27^\circ - \cot 27^\circ = \tan 9^\circ + \tan 81^\circ - \tan 27^\circ - \tan 63^\circ.\]Then
\begin{align*}
\tan 9^\circ + \tan 81^\circ - \tan 27^\circ - \tan 63^\circ &= \tan 9^\circ - \tan 27^\circ + \tan 81^\circ - \tan 63^\circ \\
&= \frac{\sin 9^\circ}{\cos 9^\circ} - \frac{\sin 27^\circ}{\cos 27^\circ} + \frac{\sin 81^\circ}{\cos 81^\circ} - \frac{\sin 63^\circ}{\cos 63^\circ} \\
&= \frac{\sin 9^\circ \cos 27^\circ - \sin 27^\circ \cos 9^\circ}{\cos 9^\circ \cos 27^\circ} + \frac{\sin 81^\circ \cos 63^\circ - \sin 63^\circ \cos 81^\circ}{\cos 81^\circ \cos 63^\circ}.
\end{align*}From the angle subtraction formula,
\begin{align*}
&\frac{\sin 9^\circ \cos 27^\circ - \sin 27^\circ \cos 9^\circ}{\cos 9^\circ \cos 27^\circ} + \frac{\sin 81^\circ \cos 63^\circ - \sin 63^\circ \cos 81^\circ}{\cos 81^\circ \cos 63^\circ} \\
&= \frac{\sin (9^\circ - 27^\circ)}{\cos 9^\circ \cos 27^\circ} + \frac{\sin (81^\circ - 63^\circ)}{\cos 81^\circ \cos 63^\circ} \\
&= -\frac{\sin 18^\circ}{\cos 9^\circ \cos 27^\circ} + \frac{\sin 18^\circ}{\cos 81^\circ \cos 63^\circ} \\
&= \sin 18^\circ \cdot \frac{\cos 9^\circ \cos 27^\circ - \cos 63^\circ \cos 81^\circ}{\cos 9^\circ \cos 27^\circ \cos 63^\circ \cos 81^\circ} \\
&= \sin 18^\circ \cdot \frac{\cos 9^\circ \cos 27^\circ - \sin 27^\circ \sin 9^\circ}{\cos 9^\circ \sin 9^\circ \cos 27^\circ \sin 27^\circ}.
\end{align*}From the angle addition formula and double angle formula,
\begin{align*}
\sin 18^\circ \cdot \frac{\cos 9^\circ \cos 27^\circ - \sin 27^\circ \sin 9^\circ}{\cos 9^\circ \sin 9^\circ \cos 27^\circ \sin 27^\circ} &= \sin 18^\circ \cdot \frac{\cos (27^\circ + 9^\circ)}{\frac{1}{2} \sin 18^\circ \cdot \frac{1}{2} \sin 54^\circ} \\
&= \frac{4 \sin 18^\circ \cos 36^\circ}{\sin 18^\circ \sin 54^\circ} \\
&= \boxed{4}.
\end{align*} | null | null | null | Level 3 | Precalculus | \(\boxed{None}\) | Simplify
\[\tan 9^\circ + \cot 9^\circ - \tan 27^\circ - \cot 27^\circ.\]
The following text is the beginning part of the answer, which you can refer to for solving the problem:
We know that $\cot 9^\circ = \tan 81^\circ$ and $\cot 27^\circ = \tan 63^\circ,$ so
\[\tan 9^\circ + \cot 9^\circ - \tan 27^\circ - \cot 27^\circ = \tan 9^\circ + \tan 81^\circ - \tan 27^\circ - \tan 63^\circ.\]Then
\begin{align*}
\tan 9^\circ + \tan 81^\circ - \tan 27^\circ - \tan 63^\circ &= \tan 9^\circ - \tan 27^\circ + \tan 81^\circ - \tan 63^\circ \\
&= \frac{\sin 9^\circ}{\cos 9^\circ} - \frac{\sin 27^\circ}{\cos 27^\circ} + \frac{\sin 81^\circ}{\cos 81^\circ} - \frac{\sin 63^\circ}{\cos 63^\circ} \\
&= \frac{\sin 9^\circ \cos 27^\circ - \sin 27^\circ \cos 9^\circ}{\cos 9^\circ \cos 27^\circ} + \frac{\sin 81^\circ \cos 63^\circ - \sin 63^\circ \cos 81^\circ}{\cos 81^\circ \cos 63^\circ}.
\end{align*}From the angle subtraction formula,
\begin{align*}
&\frac{\sin 9^\circ \cos 27^\circ - \sin 27^\circ \cos 9^\circ}{\cos 9^\circ \cos 27^\circ} + \frac{\sin 81^\circ \cos 63^\circ - \sin 63^\circ \cos 81^\circ}{\cos 81^\circ \cos 63^\circ} \\
&= \ |
In Cartesian space, three spheres centered at $(-2,5,4),$ $(2,1,4),$ and $(4,7,5)$ are all tangent to the $xy$-plane. The $xy$-plane is one of two planes tangent to all three spheres; the second plane can be written as the equation $ax + bx + cz = d$ for some real numbers $a,$ $b,$ $c,$ and $d.$ Find $\frac{c}{a}.$ | The equation for the $xy$-plane is $z = 0.$
[asy]
import three;
import solids;
size(300);
currentprojection = perspective(-2,-2,3);
draw((2,17,0)--(17,2,0)--(-8,-29,0)--(-29,-8,0)--cycle);
draw(shift((4,7,5))*surface(sphere(5)),gray(0.8));
draw(shift((-2,5,4))*surface(sphere(4)),gray(0.8));
draw(shift((2,1,4))*surface(sphere(4)),gray(0.8));
draw((2,17,6)--(17,2,6)--(-8,-29,-1)--(-29,-8,-1)--cycle);
draw((0,-29,0)--(-29,0,0));
label("$x + y = -29$", (0,-29,0), E);
[/asy]
Let $\mathbf{a} = \begin{pmatrix} -2 \\ 5 \\ 4 \end{pmatrix},$ $\mathbf{b} = \begin{pmatrix} 2 \\ 1 \\ 4 \end{pmatrix},$ and $\mathbf{c} = \begin{pmatrix} 4 \\ 7 \\ 5 \end{pmatrix}.$ Then the normal vector to the plane passing through the centers of the spheres is
\[(\mathbf{b} - \mathbf{a}) \times (\mathbf{c} - \mathbf{a}) = \begin{pmatrix} 4 \\ -4 \\ 0 \end{pmatrix} \times \begin{pmatrix} 6 \\ 2 \\ 1 \end{pmatrix} = \begin{pmatrix} -4 \\ -4 \\ 32 \end{pmatrix}.\]We can scale this vector, and take $\begin{pmatrix} 1 \\ 1 \\ -8 \end{pmatrix}$ as the normal vector. Thus, the equation of the plane is of the form $x + y - 8z = d.$ Substituting any of the centers, we find the equation of this plane is
\[x + y - 8z = -29.\]The intersection of this plane with the plane $z = 0$ is the line defined by
\[x + y = -29.\]The equation of any plane containing this line is then of the form
\[kx + ky + z = -29k.\]We want all three spheres to be tangent to this plane. Then the distance between this plane and the center $(-2,5,4)$ should be 4. From the formula for the distance between a point and a plane,
\[\frac{|-2k + 5k + 4 + 29k|}{\sqrt{k^2 + k^2 + 1}} = 4.\]Then $|32k + 4| = 4 \sqrt{2k^2 + 1},$ so $|8k + 1| = \sqrt{2k^2 + 1}.$ Squaring, we get $64k^2 + 16k + 1 = 2k^2 + 1,$ which simplifies to
\[62k^2 + 16k = 2k(31k + 8) = 0.\]The solutions are $k = 0$ and $k = -\frac{8}{31}.$ The solution $k = 0$ corresponds to the plane $z = 0,$ so the other plane corresponds to $k = -\frac{8}{31},$ which gives us the equation
\[-\frac{8}{31} x - \frac{8}{31} y + z = 29 \cdot \frac{8}{31}.\]Thus, $\frac{c}{a} = \boxed{-\frac{31}{8}}.$ | null | null | null | Level 5 | Precalculus | \(\boxed{None}\) | In Cartesian space, three spheres centered at $(-2,5,4),$ $(2,1,4),$ and $(4,7,5)$ are all tangent to the $xy$-plane. The $xy$-plane is one of two planes tangent to all three spheres; the second plane can be written as the equation $ax + bx + cz = d$ for some real numbers $a,$ $b,$ $c,$ and $d.$ Find $\frac{c}{a}.$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
The equation for the $xy$-plane is $z = 0.$
[asy]
import three;
import solids;
size(300);
currentprojection = perspective(-2,-2,3);
draw((2,17,0)--(17,2,0)--(-8,-29,0)--(-29,-8,0)--cycle);
draw(shift((4,7,5))*surface(sphere(5)),gray(0.8));
draw(shift((-2,5,4))*surface(sphere(4)),gray(0.8));
draw(shift((2,1,4))*surface(sphere(4)),gray(0.8));
draw((2,17,6)--(17,2,6)--(-8,-29,-1)--(-29,-8,-1)--cycle);
draw((0,-29,0)--(-29,0,0));
label("$x + y = -29$", (0,-29,0), E);
[/asy]
Let $\mathbf{a} = \begin{pmatrix} -2 \\ 5 \\ 4 \end{pmatrix},$ $\mathbf{b} = \begin{pmatrix} 2 \\ 1 \\ 4 \end{pmatrix},$ and $\mathbf{c} = \begin{pmatrix} 4 \\ 7 \\ 5 \end{pmatrix}.$ Then the normal vector to the plane passing through the centers of the spheres is
\[(\mathbf{b} - \mathbf{a}) \times (\mathbf{c} - \mathbf{a}) = \begin{pmatrix} 4 \\ -4 \\ 0 \end{pmatrix} \times \begin{pmatrix} 6 \\ 2 \\ 1 \end{pmatrix} = \begin{pmatrix} -4 \\ -4 \\ 32 \end{pmatrix}.\]We can scale this vector, and take $\begin{pmatrix} 1 \\ 1 \\ -8 \end{pmatrix}$ as the normal vector. Thus, t |
In triangle $ABC,$ $AB = 3$ and $AC = 5.$ Let $O$ be the circumcenter of triangle $ABC.$ Find $\overrightarrow{OA} \cdot \overrightarrow{BC}.$ | Let $\mathbf{a} = \overrightarrow{OA},$ $\mathbf{b} = \overrightarrow{OB},$ and $\mathbf{c} = \overrightarrow{OC}.$ Then
\[\overrightarrow{AB} = \overrightarrow{OB} - \overrightarrow{OA} = \mathbf{b} - \mathbf{a}.\]Similarly, $\overrightarrow{AC} = \mathbf{c} - \mathbf{a}$ and $\overrightarrow{BC} = \mathbf{c} - \mathbf{b}.$ We then want to compute
\[\overrightarrow{OA} \cdot \overrightarrow{BC} = \mathbf{a} \cdot (\mathbf{c} - \mathbf{b}) = \mathbf{a} \cdot \mathbf{c} - \mathbf{a} \cdot \mathbf{b}.\][asy]
unitsize(2 cm);
pair A, B, C, O;
A = dir(100);
B = dir(200);
C = dir(340);
O = (0,0);
draw(Circle(O,1));
draw(A--B--C--cycle);
draw(O--A,Arrow(6));
draw(O--B,Arrow(6));
draw(O--C,Arrow(6));
label("$A$", A, A);
label("$B$", B, B);
label("$C$", C, C);
label("$O$", O, NE);
label("$\mathbf{a}$", A/2, SW);
label("$\mathbf{b}$", B/2, SE);
label("$\mathbf{c}$", C/2, SW);
[/asy]
Since $AC = 5,$ $AC^2 = 25.$ But
\begin{align*}
AC^2 &= \|\mathbf{c} - \mathbf{a}\|^2 \\
&= (\mathbf{c} - \mathbf{a}) \cdot (\mathbf{c} - \mathbf{a}) \\
&= \|\mathbf{c}\|^2 - 2 \mathbf{a} \cdot \mathbf{c} + \|\mathbf{a}\|^2 \\
&= 2R^2 - 2 \mathbf{a} \cdot \mathbf{c},
\end{align*}where $R$ is the circumradius. Hence,
\[\mathbf{a} \cdot \mathbf{c} = R^2 - \frac{AC^2}{2}.\]Similarly, we can prove that
\[\mathbf{a} \cdot \mathbf{b} = R^2 - \frac{AB^2}{2}.\]Therefore,
\[\mathbf{a} \cdot \mathbf{c} - \mathbf{a} \cdot \mathbf{b} = \left( R^2 - \frac{AC^2}{2} \right) - \left( R^2 - \frac{AB^2}{2} \right) = \frac{AB^2 - AC^2}{2} = \frac{3^2 - 5^2}{2} = \boxed{-8}.\] | null | null | null | Level 5 | Precalculus | \(\boxed{None}\) | In triangle $ABC,$ $AB = 3$ and $AC = 5.$ Let $O$ be the circumcenter of triangle $ABC.$ Find $\overrightarrow{OA} \cdot \overrightarrow{BC}.$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
Let $\mathbf{a} = \overrightarrow{OA},$ $\mathbf{b} = \overrightarrow{OB},$ and $\mathbf{c} = \overrightarrow{OC}.$ Then
\[\overrightarrow{AB} = \overrightarrow{OB} - \overrightarrow{OA} = \mathbf{b} - \mathbf{a}.\]Similarly, $\overrightarrow{AC} = \mathbf{c} - \mathbf{a}$ and $\overrightarrow{BC} = \mathbf{c} - \mathbf{b}.$ We then want to compute
\[\overrightarrow{OA} \cdot \overrightarrow{BC} = \mathbf{a} \cdot (\mathbf{c} - \mathbf{b}) = \mathbf{a} \cdot \mathbf{c} - \mathbf{a} \cdot \mathbf{b}.\][asy]
unitsize(2 cm);
pair A, B, C, O;
A = dir(100);
B = dir(200);
C = dir(340);
O = (0,0);
draw(Circle(O,1));
draw(A--B--C--cycle);
draw(O--A,Arrow(6));
draw(O--B,Arrow(6));
draw(O--C,Arrow(6));
label("$A$", A, A);
label("$B$", B, B);
label("$C$", C, C);
label("$O$", |
Point $D$ is on side $\overline{BC}$ of triangle $ABC.$ If $\angle CAD = \angle BAD = 60^\circ,$ $AC = 3,$ and $AB = 6,$ then find $AD.$ | By the Angle Bisector Theorem,
\[\frac{BD}{AB} = \frac{CD}{AC},\]or $\frac{BD}{6} = \frac{AC}{3},$ so $BD = 2CD.$ Let $x = CD$; then $BD = 2x.$
[asy]
unitsize (0.8 cm);
pair A, B, C, D;
B = (0,0);
C = (3*sqrt(7),0);
A = intersectionpoint(arc(B,6,0,180),arc(C,3,0,180));
D = interp(B,C,2/3);
draw(A--B--C--cycle);
draw(A--D);
label("$A$", A, N);
label("$B$", B, SW);
label("$C$", C, SE);
label("$D$", D, S);
label("$3$", (A + C)/2, NE);
label("$6$", (A + B)/2, NW);
label("$x$", (C + D)/2, S);
label("$2x$", (B + D)/2, S);
label("$d$", (A + D)/2, W);
[/asy]
Let $d = AD.$ Then by the Law of Cosines on triangle $ABD,$
\[4x^2 = d^2 + 36 - 2 \cdot d \cdot 6 \cos 60^\circ = d^2 - 6d + 36.\]By the Law of Cosines on triangle $ACD,$
\[x^2 = d^2 + 9 - 2 \cdot d \cdot 3 \cos 60^\circ = d^2 - 3d + 9.\]Hence, $4(d^2 - 3d + 9) = d^2 - 6d + 36.$ This simplifies to $3d^2 - 6d = 3d(d - 2) = 0.$ Therefore, $d = \boxed{2}.$ | null | null | null | Level 3 | Precalculus | \(\boxed{None}\) | Point $D$ is on side $\overline{BC}$ of triangle $ABC.$ If $\angle CAD = \angle BAD = 60^\circ,$ $AC = 3,$ and $AB = 6,$ then find $AD.$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
By the Angle Bisector Theorem,
\[\frac{BD}{AB} = \frac{CD}{AC},\]or $\frac{BD}{6} = \frac{AC}{3},$ so $BD = 2CD.$ Let $x = CD$; then $BD = 2x.$
[asy]
unitsize (0.8 cm);
pair A, B, C, D;
B = (0,0);
C = (3*sqrt(7),0);
A = intersectionpoint(arc(B,6,0,180),arc(C,3,0,180));
D = interp(B,C,2/3);
draw(A--B--C--cycle);
draw(A--D);
label("$A$", A, N);
label("$B$", B, SW);
label("$C$", C, SE);
label("$D$", D, S);
label("$3$", (A + C)/2, NE);
label("$6$", (A + B |
If $\sin (\pi \cos x) = \cos (\pi \sin x),$ enter all possible values of $\sin 2x,$ separated by commas. | From the given equation,
\[\cos (\pi \sin x) = \sin (\pi \cos x) = \cos \left( \frac{\pi}{2} - \pi \cos x \right).\]This means $\pi \sin x$ and $\frac{\pi}{2} - \pi \cos x$ either add up to a multiple of $2 \pi,$ or differ by a multiple of $2 \pi.$
In the first case,
\[\pi \sin x + \frac{\pi}{2} - \pi \cos x = 2 \pi n\]for some integer $n.$ Then
\[\sin x - \cos x = 2n - \frac{1}{2}.\]Since
\[(\sin x - \cos x)^2 = \sin^2 x - 2 \sin x \cos x + \cos^2 x = 1 - \sin 2x \le 2,\]it follows that $|\sin x - \cos x| \le \sqrt{2}.$ Thus, the only possible value of $n$ is 0, in which case
\[\sin x - \cos x = -\frac{1}{2}.\]Squaring, we get
\[\sin^2 x - 2 \sin x \cos x + \cos^2 x = \frac{1}{4}.\]Then $1 - \sin 2x = \frac{1}{4},$ so $\sin 2x = \frac{3}{4}.$
In the second case,
\[\pi \sin x + \pi \cos x - \frac{\pi}{2} = 2 \pi n\]for some integer $n.$ Then
\[\sin x + \cos x = 2n + \frac{1}{2}.\]By the same reasoning as above, the only possible value of $n$ is 0, in which case
\[\sin x + \cos x = \frac{1}{2}.\]Squaring, we get
\[\sin^2 x + 2 \sin x \cos x + \cos^2 x = \frac{1}{4}.\]Then $1 + \sin 2x = \frac{1}{4},$ so $\sin 2x = -\frac{3}{4}.$
Thus, the possible values of $\sin 2x$ are $\boxed{\frac{3}{4}, -\frac{3}{4}}.$ | null | null | null | Level 5 | Precalculus | \(\boxed{None}\) | If $\sin (\pi \cos x) = \cos (\pi \sin x),$ enter all possible values of $\sin 2x,$ separated by commas.
The following text is the beginning part of the answer, which you can refer to for solving the problem:
From the given equation,
\[\cos (\pi \sin x) = \sin (\pi \cos x) = \cos \left( \frac{\pi}{2} - \pi \cos x \right).\]This means $\pi \sin x$ and $\frac{\pi}{2} - \pi \cos x$ either add up to a multiple of $2 \pi,$ or differ by a multiple of $2 \pi.$
In the first case,
\[\pi \sin x + \frac{\pi}{2} - \pi \cos x = 2 \pi n\]for some integer $n.$ Then
\[\sin x - \cos x = 2n - \frac{1}{2}.\]Since
\[(\sin x - \cos x)^2 = \sin^2 x - 2 \sin x \cos x + \cos^2 x = 1 - \sin 2x \le 2,\]it follows that $|\sin x - \cos x| \le \sqrt{2}.$ Thus, the only possible value of $n$ is 0, in which case
\[\sin x - \cos x = -\frac{1} |
Find all values of $x$ which satisfy
\[\sin (4 \arctan x) = \frac{24}{25}.\]Enter all the solutions, separated by commas. | Let $\theta = \arctan x.$ Then from the double angle formula,
\begin{align*}
\sin 4 \theta &= 2 \sin 2 \theta \cos 2 \theta \\
&= 4 \sin \theta \cos \theta (2 \cos^2 \theta - 1).
\end{align*}Since $\theta = \arctan x,$ $x = \tan \theta.$ Then $\cos \theta = \frac{1}{\sqrt{x^2 + 1}}$ and $\sin \theta = \frac{x}{\sqrt{x^2 + 1}},$ so
\begin{align*}
\sin 4 \theta &= 2 \sin \theta \cos \theta (2 \cos^2 \theta - 1) \\
&= 4 \cdot \frac{x}{\sqrt{x^2 + 1}} \cdot \frac{1}{\sqrt{x^2 + 1}} \cdot \left( 2 \cdot \frac{1}{x^2 + 1} - 1 \right) \\
&= -\frac{4x (x^2 - 1)}{(x^2 + 1)^2} = \frac{24}{25}.
\end{align*}This simplifies to
\[6x^4 + 25x^3 + 12x^2 - 25x + 6 = 0.\]This factors as $(x + 2)(x + 3)(2x - 1)(3x - 1) = 0,$ so the solutions are $\boxed{-3, -2, \frac{1}{3}, \frac{1}{2}}.$ | null | null | null | Level 4 | Precalculus | \(\boxed{None}\) | Find all values of $x$ which satisfy
\[\sin (4 \arctan x) = \frac{24}{25}.\]Enter all the solutions, separated by commas.
The following text is the beginning part of the answer, which you can refer to for solving the problem:
Let $\theta = \arctan x.$ Then from the double angle formula,
\begin{align*}
\sin 4 \theta &= 2 \sin 2 \theta \cos 2 \theta \\
&= 4 \sin \theta \cos \theta (2 \cos^2 \theta - 1).
\end{align*}Since $\theta = \arctan x,$ $x = \tan \theta.$ Then $\cos \theta = \frac{1}{\sqrt{x^2 + 1}}$ and $\sin \theta = \frac{x}{\sqrt{x^2 + 1}},$ so
\begin{align*}
\sin 4 \theta &= 2 \sin \theta \cos \thet |
Find the matrix that corresponds to reflecting over the vector $\begin{pmatrix} -1 \\ 3 \end{pmatrix}.$ | Let $\mathbf{v} = \begin{pmatrix} x \\ y \end{pmatrix},$ let $\mathbf{r}$ be the reflection of $\mathbf{v}$ over $\begin{pmatrix} -1 \\ 3 \end{pmatrix},$ and let $\mathbf{p}$ be the projection of $\mathbf{v}$ onto $\begin{pmatrix} -1 \\ 3 \end{pmatrix}.$
Note that $\mathbf{p}$ is the midpoint of $\mathbf{v}$ and $\mathbf{r}.$ Thus, we can use $\mathbf{p}$ to compute the reflection matrix.
[asy]
unitsize(1 cm);
pair D, P, R, V;
D = (-1,3);
V = (0.5,2.5);
R = reflect((0,0),D)*(V);
P = (V + R)/2;
draw((-3,0)--(2,0));
draw((0,-1)--(0,4));
draw((0,0)--D,Arrow(6));
draw((0,0)--V,red,Arrow(6));
draw((0,0)--R,blue,Arrow(6));
draw((0,0)--P,green,Arrow(6));
draw(V--R,dashed);
label("$\mathbf{p}$", P, SW);
label("$\mathbf{v}$", V, E);
label("$\mathbf{r}$", R, SW);
[/asy]
From the projection formula,
\begin{align*}
\mathbf{p} &= \operatorname{proj}_{\begin{pmatrix} -1 \\ 3 \end{pmatrix}} \begin{pmatrix} x \\ y \end{pmatrix} \\
&= \frac{\begin{pmatrix} x \\ y \end{pmatrix} \cdot \begin{pmatrix} -1 \\ 3 \end{pmatrix}}{\begin{pmatrix} -1 \\ 3 \end{pmatrix} \cdot \begin{pmatrix} -1 \\ 3 \end{pmatrix}} \begin{pmatrix} 2 \\ -3 \end{pmatrix} \\
&= \frac{-x + 3y}{10} \begin{pmatrix} -1 \\ 3 \end{pmatrix} \\
&= \begin{pmatrix} \frac{x - 3y}{10} \\ \frac{-3x + 9y}{10} \end{pmatrix}.
\end{align*}Since $\mathbf{p}$ is the midpoint of $\mathbf{v}$ and $\mathbf{r},$
\[\mathbf{p} = \frac{\mathbf{v} + \mathbf{r}}{2}.\]Then
\begin{align*}
\mathbf{r} &= 2 \mathbf{p} - \mathbf{v} \\
&= 2 \begin{pmatrix} \frac{x - 3y}{10} \\ \frac{-3x + 9y}{10} \end{pmatrix} - \begin{pmatrix} x \\ y \end{pmatrix} \\
&= \begin{pmatrix} \frac{-4x - 3y}{5} \\ \frac{-3x + 4y}{5} \end{pmatrix} \\
&= \begin{pmatrix} -4/5 & -3/5 \\ -3/5 & 4/5 \end{pmatrix} \begin{pmatrix} x \\ y \end{pmatrix}.
\end{align*}Thus, the matrix is $\boxed{\begin{pmatrix} -4/5 & -3/5 \\ -3/5 & 4/5 \end{pmatrix}}.$ | null | null | null | Level 4 | Precalculus | \(\boxed{None}\) | Find the matrix that corresponds to reflecting over the vector $\begin{pmatrix} -1 \\ 3 \end{pmatrix}.$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
Let $\mathbf{v} = \begin{pmatrix} x \\ y \end{pmatrix},$ let $\mathbf{r}$ be the reflection of $\mathbf{v}$ over $\begin{pmatrix} -1 \\ 3 \end{pmatrix},$ and let $\mathbf{p}$ be the projection of $\mathbf{v}$ onto $\begin{pmatrix} -1 \\ 3 \end{pmatrix}.$
Note that $\mathbf{p}$ is the midpoint of $\mathbf{v}$ and $\mathbf{r}.$ Thus, we can use $\mathbf{p}$ to compute the reflection matrix.
[asy]
unitsize(1 cm);
pair D, P, R, V;
D = (-1,3);
V = (0.5,2.5);
R = reflect((0,0),D)*(V);
P = (V + R)/2;
draw((-3,0)--(2,0));
draw((0,-1)--(0,4));
draw((0,0)--D,Arrow(6));
draw((0,0)--V,red,Arrow(6));
draw((0,0)--R,blue,Arrow(6));
draw((0,0)--P,green,Arrow(6));
draw(V--R,dashed);
label("$\mathbf{p}$", P, SW);
label("$\mathbf{v}$", V, E);
label("$\mathbf{r}$", R, SW);
[/asy]
From the projection formula,
\begin{align*}
\mathbf{p} &= \operatorname{proj}_{\begin{pmatrix} -1 \\ 3 \end{pmatrix}} \begin{pmatrix} x \\ y \end{pmatrix} \\
& |
Find the matrix $\mathbf{M}$ such that
\[\mathbf{M} \begin{pmatrix} 1 & -2 \\ 1 & 4 \end{pmatrix} = \begin{pmatrix} 6 & 0 \\ 0 & 6 \end{pmatrix}.\] | The inverse of $\begin{pmatrix} 1 & -2 \\ 1 & 4 \end{pmatrix}$ is
\[\frac{1}{(1)(4) - (-2)(1)} \begin{pmatrix} 4 & 2 \\ -1 & 1 \end{pmatrix} = \frac{1}{6} \begin{pmatrix} 4 & 2 \\ -1 & 1 \end{pmatrix}.\]So, multiplying by this inverse on the right, we get
\[\mathbf{M} = \begin{pmatrix} 6 & 0 \\ 0 & 6 \end{pmatrix} \cdot \frac{1}{6} \begin{pmatrix} 4 & 2 \\ -1 & 1 \end{pmatrix} = \boxed{\begin{pmatrix} 4 & 2 \\ -1 & 1 \end{pmatrix}}.\] | null | null | null | Level 3 | Precalculus | \(\boxed{None}\) | Find the matrix $\mathbf{M}$ such that
\[\mathbf{M} \begin{pmatrix} 1 & -2 \\ 1 & 4 \end{pmatrix} = \begin{pmatrix} 6 & 0 \\ 0 & 6 \end{pmatrix}.\]
The following text is the beginning part of the answer, which you can refer to for solving the problem:
The inverse of $\begin{pmatrix} 1 & -2 \\ 1 & 4 \end{pmatrix}$ is
\[\frac{1}{(1)(4) - (-2)(1)} \begin{pmatrix} 4 & 2 \\ -1 & 1 \end{pmatrix} = \frac{1}{6} \begin{pmatrix} 4 & 2 \\ -1 & 1 \end{pmatrix}.\]So, multiplying |
Find the matrix $\mathbf{M}$ that swaps the rows of a matrix. In other words,
\[\mathbf{M} \begin{pmatrix} a & b \\ c & d \end{pmatrix} = \begin{pmatrix} c & d \\ a & b \end{pmatrix}.\]If no such matrix $\mathbf{M}$ exists, then enter the zero matrix. | Let $\mathbf{M} = \begin{pmatrix} p & q \\ r & s \end{pmatrix}.$ Then
\[\mathbf{M} \begin{pmatrix} a & b \\ c & d \end{pmatrix} = \begin{pmatrix} p & q \\ r & s \end{pmatrix} \begin{pmatrix} a & b \\ c & d \end{pmatrix} = \begin{pmatrix} pa + qc & pb + qd \\ ra + sc & rb + sd \end{pmatrix}.\]We want this to be equal to $\begin{pmatrix} c & d \\ a & b \end{pmatrix}.$ We can achieve this by taking $p = 0,$ $q = 1,$ $r = 1,$ and $s = 0,$ so $\mathbf{M} = \boxed{\begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix}}.$ | null | null | null | Level 3 | Precalculus | \(\boxed{None}\) | Find the matrix $\mathbf{M}$ that swaps the rows of a matrix. In other words,
\[\mathbf{M} \begin{pmatrix} a & b \\ c & d \end{pmatrix} = \begin{pmatrix} c & d \\ a & b \end{pmatrix}.\]If no such matrix $\mathbf{M}$ exists, then enter the zero matrix.
The following text is the beginning part of the answer, which you can refer to for solving the problem:
Let $\mathbf{M} = \begin{pmatrix} p & q \\ r & s \end{pmatrix}.$ Then
\[\mathbf{M} \begin{pmatrix} a & b \\ c & d \end{pmatrix} = \begin{pmatrix} p & q \\ r & s \end{pmatrix} \begin{pmatrix} a & b \\ c & d \end{pmatrix} = \begin{pmatrix} pa + qc & pb + qd |
In triangle $ABC,$
\[\tan \left( \frac{B - C}{2} \right) \tan \frac{A}{2} = \frac{1}{29} \quad \text{and} \quad \tan \left( \frac{C - A}{2} \right) \tan \frac{B}{2} = \frac{1}{27}.\]Find $\tan \left( \frac{A - B}{2} \right) \tan \frac{C}{2}.$ | We can write
\begin{align*}
\tan \left( \frac{B - C}{2} \right) \tan \frac{A}{2} &= \frac{\sin (\frac{B - C}{2}) \sin \frac{A}{2}}{\cos (\frac{B - C}{2}) \cos \frac{A}{2}} \\
&= \frac{\cos (\frac{A + C - B}{2}) - \cos (\frac{A + B - C}{2})}{\cos (\frac{A + B - C}{2}) + \cos (\frac{A + C - B}{2})} \\
&= \frac{\cos (90^\circ - B) - \cos (90^\circ - C)}{\cos (90^\circ - C) + \cos (90^\circ - B)} \\
&= \frac{\sin B - \sin C}{\sin C + \sin B}.
\end{align*}As usual, let $a = BC,$ $b = AC,$ and $c = AB.$ By the Law of Sines, $\frac{b}{\sin B} = \frac{c}{\sin C},$ so
\[\frac{\sin B - \sin C}{\sin C + \sin B} = \frac{b - c}{b + c} = \frac{1}{29}.\]Then $29b - 29c = b + c,$ so $28b = 30c,$ or $\frac{b}{15} = \frac{c}{14}.$
Similarly, we can show that
\[\tan \left( \frac{C - A}{2} \right) \tan \frac{B}{2} = \frac{c - a}{c + a},\]so $\frac{c - a}{c + a} = \frac{1}{27}.$ Then $27c - 27a = c + a,$ so $26c = 28a,$ or $\frac{a}{13} = \frac{c}{14}.$
Finally,
\[\tan \left( \frac{A - B}{2} \right) \tan \frac{C}{2} = \frac{a - b}{a + b} = \frac{13 - 15}{13 + 15} = \frac{-2}{28} = \boxed{-\frac{1}{14}}.\] | null | null | null | Level 5 | Precalculus | \(\boxed{None}\) | In triangle $ABC,$
\[\tan \left( \frac{B - C}{2} \right) \tan \frac{A}{2} = \frac{1}{29} \quad \text{and} \quad \tan \left( \frac{C - A}{2} \right) \tan \frac{B}{2} = \frac{1}{27}.\]Find $\tan \left( \frac{A - B}{2} \right) \tan \frac{C}{2}.$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
We can write
\begin{align*}
\tan \left( \frac{B - C}{2} \right) \tan \frac{A}{2} &= \frac{\sin (\frac{B - C}{2}) \sin \frac{A}{2}}{\cos (\frac{B - C}{2}) \cos \frac{A}{2}} \\
&= \frac{\cos (\frac{A + C - B}{2}) - \cos (\frac{A + B - C}{2})}{\cos (\frac{A + B - C}{2}) + \cos (\frac{A + C - B}{2})} \\
&= \frac{\cos (90^\circ - B) - \cos (90^\circ - C)}{\cos (90^\circ - C) + \cos (90^\circ - B)} \\
&= \frac{\sin B - \sin C}{\sin C + \sin B}.
\end{align*}As usual, let $a = BC,$ $b = AC,$ and $c = AB.$ By the Law of Sines, $\frac{b}{\sin B} = \frac{c |
In triangle $ABC,$ $\angle A,$ $\angle B,$ and $\angle C$ form an arithmetic sequence. The length of the altitude from $B$ to $\overline{AC}$ is equal to $AB - BC.$ Find all possible values of
\[\sin \frac{C - A}{2}.\]Enter all possible values, separated by commas. | Since $\angle A,$ $\angle B,$ $\angle C$ form an arithmetic sequence, $2 \angle B = \angle A + \angle C.$ Then
\[3 \angle B = \angle A + \angle B + \angle C = 180^\circ,\]which means $\angle B = 60^\circ,$ and $\angle A + \angle C = 120^\circ.$
Let $h$ be the altitude from $B.$
[asy]
unitsize (1 cm);
pair A, B, C, D;
A = (0,0);
B = 5*dir(40);
C = (5,0);
D = (B.x,0);
draw(A--B--C--cycle);
draw(B--D);
label("$A$", A, SW);
label("$B$", B, N);
label("$C$", C, SE);
label("$h$", (B + D)/2, E);
[/asy]
Then
\[h = AB - BC = \frac{h}{\sin A} - \frac{h}{\sin C},\]so $1 = \frac{1}{\sin A} - \frac{1}{\sin C}.$ Hence,
\[\sin C - \sin A = \sin A \sin C.\]We can write this as
\[2 \sin \frac{C - A}{2} \cos \frac{A + C}{2} = \frac{\cos (A - C) - \cos (A + C)}{2}.\]Since $A + C = 120^\circ,$
\[\sin \frac{C - A}{2} = \frac{\cos (A - C) + \frac{1}{2}}{2} = \frac{\cos (C - A) + \frac{1}{2}}{2}.\]Then
\begin{align*}
4 \sin \frac{C - A}{2} &= 2 \cos (C - A) + 1 \\
&= 2 \left( 1 - 2 \sin^2 \frac{C - A}{2} \right) + 1 \\
&= 3 - 4 \sin^2 \frac{C - A}{2},
\end{align*}so
\[4 \sin^2 \frac{C - A}{2} + 4 \sin \frac{C - A}{2} - 3 = 0.\]This factors as
\[\left( 2 \sin \frac{C - A}{2} - 1 \right) \left( 2 \sin \frac{C - A}{2} + 3 \right) = 0.\]Thus, the only possible value of $\sin \frac{C - A}{2}$ is $\boxed{\frac{1}{2}}.$ | null | null | null | Level 5 | Precalculus | \(\boxed{None}\) | In triangle $ABC,$ $\angle A,$ $\angle B,$ and $\angle C$ form an arithmetic sequence. The length of the altitude from $B$ to $\overline{AC}$ is equal to $AB - BC.$ Find all possible values of
\[\sin \frac{C - A}{2}.\]Enter all possible values, separated by commas.
The following text is the beginning part of the answer, which you can refer to for solving the problem:
Since $\angle A,$ $\angle B,$ $\angle C$ form an arithmetic sequence, $2 \angle B = \angle A + \angle C.$ Then
\[3 \angle B = \angle A + \angle B + \angle C = 180^\circ,\]which means $\angle B = 60^\circ,$ and $\angle A + \angle C = 120^\circ.$
Let $h$ be the altitude from $B.$
[asy]
unitsize (1 cm);
pair A, B, C, D;
A = (0,0);
B = 5*dir(40);
C = (5,0);
D = (B.x,0);
draw(A--B--C--cycle);
draw(B--D);
label("$A$", A, SW);
label("$B$", B, N);
label("$C$", C, SE);
label("$h$", (B + D)/2, E);
[/asy]
Then
\[h = AB - BC = \frac{h}{\sin A} - \frac{h}{\sin C},\]so $1 = \frac{1}{\sin A} - \frac{1}{\sin C}.$ Hence,
\[\sin C - \sin A = \sin A \sin C.\]We |
Let $\mathbf{a},$ $\mathbf{b},$ $\mathbf{c}$ be vectors such that $\|\mathbf{a}\| = 2,$ $\|\mathbf{b}\| = 3,$ and
\[\mathbf{c} \times \mathbf{a} = \mathbf{b}.\]Find the smallest possible value of $\|\mathbf{c} - \mathbf{a}\|.$ | Let $\theta$ be the angle between $\mathbf{a}$ and $\mathbf{c},$ so
\[\|\mathbf{c} \times \mathbf{a}\| = \|\mathbf{a}\| \|\mathbf{c}\| \sin \theta.\]Then $3 = 2 \|\mathbf{c}\| \sin \theta,$ so $\|\mathbf{c}\| = \frac{3}{2 \sin \theta}.$
Hence,
\begin{align*}
\|\mathbf{c} - \mathbf{a}\|^2 &= \|\mathbf{c}\|^2 - 2 \mathbf{a} \cdot \mathbf{c} + \|\mathbf{a}\|^2 \\
&= \frac{9}{4 \sin^2 \theta} - 2 \|\mathbf{a}\| \|\mathbf{c}\| \cos \theta + 4 \\
&= \frac{9}{4 \sin^2 \theta} - 2 \cdot 2 \cdot \frac{3}{2 \sin \theta} \cdot \cos \theta + 4 \\
&= \frac{9}{4 \sin^2 \theta} - \frac{6 \cos \theta}{\sin \theta} + 4.
\end{align*}We can express this in terms of $\cot \theta$:
\begin{align*}
\frac{9}{4 \sin^2 \theta} - \frac{6 \cos \theta}{\sin \theta} + 4 &= \frac{9 (\sin^2 \theta + \cos^2 \theta)}{4 \sin^2 \theta} - 6 \cot \theta + 4 \\
&= \frac{9}{4} + \frac{9}{4} \cot^2 \theta - 6 \cot \theta + 4 \\
&= \frac{9}{4} \cot^2 \theta - 6 \cot \theta + \frac{25}{4}.
\end{align*}Completing the square in $\cot \theta,$ we get
\[\|\mathbf{c} - \mathbf{a}\|^2 = \left( \frac{3}{2} \cot \theta - 2 \right)^2 + \frac{9}{4}.\]Hence, the smallest possible value of $\|\mathbf{c} - \mathbf{a}\|$ is $\boxed{\frac{3}{2}},$ which is achieved when $\cot \theta = \frac{4}{3},$ or $\tan \theta = \frac{3}{4}.$ | null | null | null | Level 5 | Precalculus | \(\boxed{None}\) | Let $\mathbf{a},$ $\mathbf{b},$ $\mathbf{c}$ be vectors such that $\|\mathbf{a}\| = 2,$ $\|\mathbf{b}\| = 3,$ and
\[\mathbf{c} \times \mathbf{a} = \mathbf{b}.\]Find the smallest possible value of $\|\mathbf{c} - \mathbf{a}\|.$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
Let $\theta$ be the angle between $\mathbf{a}$ and $\mathbf{c},$ so
\[\|\mathbf{c} \times \mathbf{a}\| = \|\mathbf{a}\| \|\mathbf{c}\| \sin \theta.\]Then $3 = 2 \|\mathbf{c}\| \sin \theta,$ so $\|\mathbf{c}\| = \frac{3}{2 \sin \theta}.$
Hence,
\begin{align*}
\|\mathbf{c} - \mathbf{a}\|^2 &= \|\mathbf{c}\|^2 - 2 \mathbf{a} \cdot \mathbf{c} + \|\mathbf{a}\|^2 \\
&= \frac{9}{4 \sin^2 \theta} - 2 \|\mathbf{a}\| \|\mathbf{c}\| \cos \theta + 4 \\
&= \frac{9}{4 \sin^2 \theta} - 2 \cdot 2 \cdot \frac{3}{2 \sin \theta} \cdot \cos \theta + 4 \\
&= \frac{9}{4 \sin^2 \theta} - \frac{6 \cos \theta}{\sin \theta} + 4.
\end{align*}We can express this in |
The matrix $\mathbf{M}$ satisfies
\[\mathbf{M} \begin{pmatrix} 2 \\ 1 \end{pmatrix} = \begin{pmatrix} 5 \\ 4 \end{pmatrix} \quad \text{and} \quad \mathbf{M} \begin{pmatrix} 3 \\ 0 \end{pmatrix} = \begin{pmatrix} 1 \\ 2 \end{pmatrix} \quad.\]Find $\det \mathbf{M}.$ | The signed area of the parallelogram generated by $\begin{pmatrix} 2 \\ 1 \end{pmatrix}$ and $\begin{pmatrix} 3 \\ 0 \end{pmatrix}$ is
\[\begin{vmatrix} 2 & 3 \\ 1 & 0 \end{vmatrix} = (2)(0) - (3)(1) = -3,\]and the signed area of the parallelogram generated by $\begin{pmatrix} 5 \\ 4 \end{pmatrix}$ and $\begin{pmatrix} 1 \\ 2 \end{pmatrix}$ is
\[\begin{vmatrix} 5 & 1 \\ 4 & 2 \end{vmatrix} = (5)(2) - (1)(4) = 6.\]Therefore, $\det \mathbf{M} = \frac{6}{-3} = \boxed{-2}.$ | null | null | null | Level 3 | Precalculus | \(\boxed{None}\) | The matrix $\mathbf{M}$ satisfies
\[\mathbf{M} \begin{pmatrix} 2 \\ 1 \end{pmatrix} = \begin{pmatrix} 5 \\ 4 \end{pmatrix} \quad \text{and} \quad \mathbf{M} \begin{pmatrix} 3 \\ 0 \end{pmatrix} = \begin{pmatrix} 1 \\ 2 \end{pmatrix} \quad.\]Find $\det \mathbf{M}.$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
The signed area of the parallelogram generated by $\begin{pmatrix} 2 \\ 1 \end{pmatrix}$ and $\begin{pmatrix} 3 \\ 0 \end{pmatrix}$ is
\[\begin{vmatrix} 2 & 3 \\ 1 & 0 \end{vmatrix} = (2)(0) - (3)(1) = -3,\]and the signed area of the par |
For positive real numbers $x$ and $y,$ the equation
\[\arctan x + \arccos \frac{y}{\sqrt{1 + y^2}} = \arcsin \frac{3}{\sqrt{10}}\]reduces to an equation of the form
\[xy + ax + by + c = 0.\]Enter the ordered triple $(a,b,c).$ | With the usual approach of constructing a right triangle, we can derive that $\arccos \frac{y}{\sqrt{1 + y^2}} = \arctan \frac{1}{y}$ and $\arcsin \frac{3}{\sqrt{10}} = \arctan 3,$ so
\[\arctan x + \arctan \frac{1}{y} = \arctan 3.\]Then
\[\tan \left( \arctan x + \arctan \frac{1}{y} \right) = 3,\]so from the angle addition formula,
\[\frac{x + \frac{1}{y}}{1 - \frac{x}{y}} = 3.\]This becomes $xy + 3x - 3y + 1 = 0,$ so $(a,b,c) = \boxed{(3,-3,1)}.$ | null | null | null | Level 5 | Precalculus | \(\boxed{None}\) | For positive real numbers $x$ and $y,$ the equation
\[\arctan x + \arccos \frac{y}{\sqrt{1 + y^2}} = \arcsin \frac{3}{\sqrt{10}}\]reduces to an equation of the form
\[xy + ax + by + c = 0.\]Enter the ordered triple $(a,b,c).$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
With the usual approach of constructing a right triangle, we can derive that $\arccos \frac{y}{\sqrt{1 + y^2}} = \arctan \frac{1}{y}$ and $\arcsin \frac{3}{\sqrt{10}} = \arctan 3,$ so
\[\arctan x + \arctan \frac{1}{y} = \arct |
Find the matrix $\mathbf{R}$ such that for any vector $\mathbf{v},$ $\mathbf{R} \mathbf{v}$ is the reflection of $\mathbf{v}$ through the $xy$-plane. | Geometrically, we see that
\[\mathbf{P} \mathbf{i} = \begin{pmatrix} 1 \\ 0 \\ 0 \end{pmatrix}, \quad \mathbf{P} \mathbf{j} = \begin{pmatrix} 0 \\ 1 \\ 0 \end{pmatrix}, \quad \mathbf{P} \mathbf{k} = \begin{pmatrix} 0 \\ 0 \\ -1 \end{pmatrix},\]so
\[\mathbf{P} = \boxed{\begin{pmatrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & -1 \end{pmatrix}}.\] | null | null | null | Level 4 | Precalculus | \(\boxed{None}\) | Find the matrix $\mathbf{R}$ such that for any vector $\mathbf{v},$ $\mathbf{R} \mathbf{v}$ is the reflection of $\mathbf{v}$ through the $xy$-plane.
The following text is the beginning part of the answer, which you can refer to for solving the problem:
Geometrically, we see that
\[\mathbf{P} \mathbf{i} = \begin{pmatrix} 1 \\ 0 \\ 0 \end{pmatrix}, \quad \mathbf{P} \mathbf{j} = \begin{pmatrix} 0 \\ 1 \\ 0 \end{pmatrix}, \ |
Let $a,$ $b,$ $c$ be nonzero real numbers. Find the maximum angle between the vectors $\begin{pmatrix} a \\ b \\ c \end{pmatrix}$ and $\begin{pmatrix} b \\ c \\ a \end{pmatrix},$ in degrees. | Let $\theta$ be the angle between the two vectors. Then
\[\cos \theta = \frac{\begin{pmatrix} a \\ b \\ c \end{pmatrix} \cdot \begin{pmatrix} b \\ c \\ a \end{pmatrix}}{\left\| \begin{pmatrix} a \\ b \\ c \end{pmatrix} \right\| \left\|\begin{pmatrix} b \\ c \\ a \end{pmatrix} \right\|} = \frac{ab + ac + bc}{a^2 + b^2 + c^2}.\]We can say that
\[(a + b + c)^2 = a^2 + b^2 + c^2 + 2(ab + ac + bc) \ge 0,\]so $2(ab + ac + bc) \ge -(a^2 + b^2 + c^2).$ Since $a,$ $b,$ and $c$ are nonzero, $a^2 + b^2 + c^2 > 0,$ so
\[\frac{2(ab + ac + bc)}{a^2 + b^2 + c^2} \ge -1.\]Hence,
\[\cos \theta = \frac{ab + ac + bc}{a^2 + b^2 + c^2} \ge -\frac{1}{2}.\]The largest angle $\theta$ that satisfies this is $\boxed{120^\circ}.$ Equality occurs for any nonzero real numbers $a,$ $b,$ $c$ that satisfy $a + b + c = 0.$ | null | null | null | Level 4 | Precalculus | \(\boxed{None}\) | Let $a,$ $b,$ $c$ be nonzero real numbers. Find the maximum angle between the vectors $\begin{pmatrix} a \\ b \\ c \end{pmatrix}$ and $\begin{pmatrix} b \\ c \\ a \end{pmatrix},$ in degrees.
The following text is the beginning part of the answer, which you can refer to for solving the problem:
Let $\theta$ be the angle between the two vectors. Then
\[\cos \theta = \frac{\begin{pmatrix} a \\ b \\ c \end{pmatrix} \cdot \begin{pmatrix} b \\ c \\ a \end{pmatrix}}{\left\| \begin{pmatrix} a \\ b \\ c \end{pmatrix} \right\| \left\|\begin{pmatrix} b \\ c \\ a \end{pmatrix} \right\|} = \frac{ab + ac + bc}{a^2 + b^2 + c^2}.\]We can say that
\[(a + b + c)^2 = a^2 + b^2 + c^2 + 2(ab + ac + bc) \ge 0 |
Convert the point $( 1, -1, -6 )$ in rectangular coordinates to cylindrical coordinates. Enter your answer in the form $(r,\theta,z),$ where $r > 0$ and $0 \le \theta < 2 \pi.$ | We have that $r = \sqrt{1^2 + (-1)^2} = \sqrt{2}.$ We want $\theta$ to satisfy
\begin{align*}
1 &= \sqrt{2} \cos \theta, \\
-1&= \sqrt{2} \sin \theta.
\end{align*}Thus, $\theta = \frac{7 \pi}{4},$ so the cylindrical coordinates are $\boxed{\left( \sqrt{2}, \frac{7 \pi}{4}, -6 \right)}.$ | null | null | null | Level 4 | Precalculus | \(\boxed{None}\) | Convert the point $( 1, -1, -6 )$ in rectangular coordinates to cylindrical coordinates. Enter your answer in the form $(r,\theta,z),$ where $r > 0$ and $0 \le \theta < 2 \pi.$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
We have that $r = \sqrt{1^2 + (-1)^2} = \sqrt{2}.$ We want $\theta$ to satisfy
\begin{align*}
1 &= \sqrt{2} \cos \theta, \\
-1&= \sqrt{2} \sin |
Let $\mathbf{a}$ and $\mathbf{b}$ be two nonzero vectors such that $\mathbf{a} + \mathbf{b}$ and $\mathbf{b}$ are orthogonal, and $\mathbf{a} + 2 \mathbf{b}$ and $\mathbf{a}$ are orthogonal. Find $\frac{\|\mathbf{a}\|}{\|\mathbf{b}\|}.$ | Since $\mathbf{a} + \mathbf{b}$ and $\mathbf{b}$ are orthogonal,
\[(\mathbf{a} + \mathbf{b}) \cdot \mathbf{b} = \mathbf{a} \cdot \mathbf{b} + \mathbf{b} \cdot \mathbf{b} = 0.\]Since $\mathbf{a} + 2 \mathbf{b}$ and $\mathbf{a}$ are orthogonal,
\[(\mathbf{a} + 2 \mathbf{b}) \cdot \mathbf{a} = \mathbf{a} \cdot \mathbf{a} + 2 \mathbf{a} \cdot \mathbf{b} = 0.\]Then
\[\mathbf{a} \cdot \mathbf{a} = -2 \mathbf{a} \cdot \mathbf{b} = 2 \mathbf{b} \cdot \mathbf{b}.\]Hence, $\|\mathbf{a}\|^2 = 2 \|\mathbf{b}\|^2,$ so
\[\frac{\|\mathbf{a}\|}{\|\mathbf{b}\|} = \boxed{\sqrt{2}}.\] | null | null | null | Level 3 | Precalculus | \(\boxed{None}\) | Let $\mathbf{a}$ and $\mathbf{b}$ be two nonzero vectors such that $\mathbf{a} + \mathbf{b}$ and $\mathbf{b}$ are orthogonal, and $\mathbf{a} + 2 \mathbf{b}$ and $\mathbf{a}$ are orthogonal. Find $\frac{\|\mathbf{a}\|}{\|\mathbf{b}\|}.$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
Since $\mathbf{a} + \mathbf{b}$ and $\mathbf{b}$ are orthogonal,
\[(\mathbf{a} + \mathbf{b}) \cdot \mathbf{b} = \mathbf{a} \cdot \mathbf{b} + \mathbf{b} \cdot \mathbf{b} = 0.\]Since $\mathbf{a} + 2 \mathbf{b}$ and $\mathbf{a}$ are orthogonal,
\[(\mathbf{a} + 2 \mathbf{b}) \cdot \mathbf |
Given $\|\mathbf{v}\| = 5$ and $\|\mathbf{w}\| = 8,$ find the largest possible value of
\[\|\operatorname{proj}_{\mathbf{w}} \mathbf{v}\|.\] | Note that
\begin{align*}
\operatorname{proj}_{\mathbf{w}} \mathbf{v} &= \left\| \frac{\mathbf{v} \cdot \mathbf{w}}{\|\mathbf{w}\|^2} \mathbf{w} \right\| \\
&= \frac{|\mathbf{v} \cdot \mathbf{w}|}{\|\mathbf{w}\|^2} \cdot \|\mathbf{w}\| \\
&= \frac{|\mathbf{v} \cdot \mathbf{w}|}{\|\mathbf{w}\|}.
\end{align*}Let $\theta$ be the angle between $\mathbf{v}$ and $\mathbf{w}.$ Then $\mathbf{v} \cdot \mathbf{w} = \|\mathbf{v}\| \|\mathbf{w}\| \cos \theta,$ so
\[\frac{|\mathbf{v} \cdot \mathbf{w}|}{\|\mathbf{w}\|} = \frac{|\|\mathbf{v}\| \|\mathbf{w}\| \cos \theta|}{\|\mathbf{w}\|} = \|\mathbf{v}\| |\cos \theta| = 5 |\cos \theta| \le 5.\]Equality occurs when $\theta = 0,$ or when $\mathbf{v}$ and $\mathbf{w}$ point in the same direction, so the largest possible value is $\boxed{5}.$
If $\mathbf{p}$ is the projection of $\mathbf{v}$ onto $\mathbf{w},$ then the length of $\mathbf{p}$ is the leg of a right triangle that has the length of $\mathbf{v}$ as the hypotenuse. Thus, geometrically, $\|\mathbf{p}\| \le \|\mathbf{v}\| = 5.$
[asy]
unitsize(1 cm);
pair O, P, V, W;
O = (0,0);
V = (10/7,sqrt(3^2 - (10/7)^2));
P = (10/7,0);
W = (7,0);
draw(O--V,Arrow(6));
draw(O--W,Arrow(6));
draw(O--P,red,Arrow(6));
draw(P--V,dashed);
label("$\mathbf{v}$", V, N);
label("$\mathbf{w}$", W, E);
label("$\mathbf{p}$", P, S);
[/asy] | null | null | null | Level 3 | Precalculus | \(\boxed{None}\) | Given $\|\mathbf{v}\| = 5$ and $\|\mathbf{w}\| = 8,$ find the largest possible value of
\[\|\operatorname{proj}_{\mathbf{w}} \mathbf{v}\|.\]
The following text is the beginning part of the answer, which you can refer to for solving the problem:
Note that
\begin{align*}
\operatorname{proj}_{\mathbf{w}} \mathbf{v} &= \left\| \frac{\mathbf{v} \cdot \mathbf{w}}{\|\mathbf{w}\|^2} \mathbf{w} \right\| \\
&= \frac{|\mathbf{v} \cdot \mathbf{w}|}{\|\mathbf{w}\|^2} \cdot \|\mathbf{w}\| \\
&= \frac{|\mathbf{v} \cdot \mathbf{w}|}{\|\mathbf{w}\|}.
\end{align*}Let $\theta$ be the angle between $\mathbf{v}$ and $\mathbf{w}.$ Then $\mathbf{v} \cdot \mathbf{w} = \|\mathbf{v}\| \|\mathbf{w}\| \cos \theta,$ so
\[\frac{|\mathbf{v} \cdot \mathbf{w}|}{\|\mathbf{w}\|} = \frac{|\|\mathbf{v}\| \|\mathbf{w}\| \cos \theta|}{\|\mathbf{w}\|} = \|\mathbf{v}\| |\cos \theta| = 5 |\cos \theta| \le 5.\]Equality occurs when $\thet |
Let $\mathbf{a}$ and $\mathbf{b}$ be orthogonal vectors. If $\operatorname{proj}_{\mathbf{a}} \begin{pmatrix} 0 \\ 13 \end{pmatrix} = \begin{pmatrix} 6 \\ 4 \end{pmatrix},$ then find $\operatorname{proj}_{\mathbf{b}} \begin{pmatrix} 0 \\ 13 \end{pmatrix}.$ | Since $\begin{pmatrix} 6 \\ 4 \end{pmatrix}$ is the projection of $\begin{pmatrix} 0 \\ 13 \end{pmatrix}$ onto $\mathbf{a},$
\[\begin{pmatrix} 0 \\ 13 \end{pmatrix} - \begin{pmatrix} 6 \\ 4 \end{pmatrix} = \begin{pmatrix} -6 \\ 9 \end{pmatrix}\]is orthogonal to $\mathbf{a}.$ But since $\mathbf{a}$ and $\mathbf{b}$ are orthogonal, $\begin{pmatrix} -6 \\ 9 \end{pmatrix}$ is a scalar multiple of $\mathbf{b}.$
[asy]
usepackage("amsmath");
unitsize(0.4 cm);
pair A, B, O, P, Q, V;
A = (3,2);
B = (2,-3);
O = (0,0);
V = (0,13);
P = (V + reflect(O,A)*(V))/2;
draw(O--V,Arrow(6));
draw(O--P,Arrow(6));
draw(P--V,Arrow(6));
draw((-1,0)--(7,0));
draw((0,-1)--(0,15));
label("$\begin{pmatrix} 0 \\ 13 \end{pmatrix}$", V, W);
label("$\begin{pmatrix} 6 \\ 4 \end{pmatrix}$", P, E);
[/asy]
Furthermore,
\[\begin{pmatrix} 0 \\ 13 \end{pmatrix} - \begin{pmatrix} -6 \\ 9 \end{pmatrix} = \begin{pmatrix} 6 \\ 4 \end{pmatrix}\]is a scalar multiple of $\mathbf{a},$ and therefore orthogonal to $\mathbf{b}.$ Hence, $\operatorname{proj}_{\mathbf{b}} \begin{pmatrix} 0 \\ 13 \end{pmatrix} = \boxed{\begin{pmatrix} -6 \\ 9 \end{pmatrix}}.$ | null | null | null | Level 5 | Precalculus | \(\boxed{None}\) | Let $\mathbf{a}$ and $\mathbf{b}$ be orthogonal vectors. If $\operatorname{proj}_{\mathbf{a}} \begin{pmatrix} 0 \\ 13 \end{pmatrix} = \begin{pmatrix} 6 \\ 4 \end{pmatrix},$ then find $\operatorname{proj}_{\mathbf{b}} \begin{pmatrix} 0 \\ 13 \end{pmatrix}.$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
Since $\begin{pmatrix} 6 \\ 4 \end{pmatrix}$ is the projection of $\begin{pmatrix} 0 \\ 13 \end{pmatrix}$ onto $\mathbf{a},$
\[\begin{pmatrix} 0 \\ 13 \end{pmatrix} - \begin{pmatrix} 6 \\ 4 \end{pmatrix} = \begin{pmatrix} -6 \\ 9 \end{pmatrix}\]is orthogonal to $\mathbf{a}.$ But since $\mathbf{a}$ and $\mathbf{b}$ are orthogonal, $\begin{pmatrix} -6 \\ 9 \end{pmatrix}$ is a scalar multiple of $\mathbf{b}.$
[asy]
usepackage("amsmath");
unitsize(0.4 cm);
pair A, B, O, P, Q, V;
A = (3,2);
B = (2,-3);
O = (0,0);
V = (0,13);
P = (V + reflect(O,A)*(V))/2;
dra |
If $0^\circ < x < 180^\circ$ and $\cos x + \sin x = \frac{1}{2},$ then $\tan x$ can be expressed in the form $-\frac{a + \sqrt{b}}{c}$ when simplified, where $a,$ $b,$ and $c$ are positive integers. Find $a + b + c.$ | From the given equation, $\cos x = \frac{1}{2} - \sin x.$ Substituting into $\cos^2 x + \sin^2 x = 1,$ we get
\[\frac{1}{4} - \sin x + \sin^2 x + \sin^2 x = 1.\]This simplifies to $8 \sin^2 x - 4 \sin x - 3 = 0.$ By the quadratic formula,
\[\sin x = \frac{1 \pm \sqrt{7}}{4}.\]Since $0^\circ < x < 180^\circ,$ $\sin x$ is positive. Hence,
\[\sin x = \frac{1 + \sqrt{7}}{4}.\]Then
\[\cos x = \frac{1}{2} - \sin x = \frac{1 - \sqrt{7}}{4},\]so
\begin{align*}
\tan x &= \frac{\sin x}{\cos x} \\
&= \frac{1 + \sqrt{7}}{1 - \sqrt{7}} \\
&= \frac{(1 + \sqrt{7})(1 + \sqrt{7})}{(1 - \sqrt{7})(1 + \sqrt{7})} \\
&= \frac{1 + 2 \sqrt{7} + 7}{-6} \\
&= -\frac{8 + 2 \sqrt{7}}{6} \\
&= -\frac{4 + \sqrt{7}}{3}.
\end{align*}Thus, $a + b + c = 4 + 7 + 3 = \boxed{14}.$ | null | null | null | Level 5 | Precalculus | \(\boxed{None}\) | If $0^\circ < x < 180^\circ$ and $\cos x + \sin x = \frac{1}{2},$ then $\tan x$ can be expressed in the form $-\frac{a + \sqrt{b}}{c}$ when simplified, where $a,$ $b,$ and $c$ are positive integers. Find $a + b + c.$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
From the given equation, $\cos x = \frac{1}{2} - \sin x.$ Substituting into $\cos^2 x + \sin^2 x = 1,$ we get
\[\frac{1}{4} - \sin x + \sin^2 x + \sin^2 x = 1.\]This simplifies to $8 \sin^2 x - 4 \sin x - 3 = 0.$ By the quadratic formula,
\[\sin x = \frac{1 \pm \sqrt{7}}{4}.\]Since $0^\circ < x < 180^\circ,$ $\sin x$ is positive. Hence,
\[\sin x = \frac{1 + \sqrt{7}}{4}.\]T |
Find the solutions to
\[\frac{1}{x - \tan 20^{\circ}} + \frac{1}{x + \tan 40^{\circ}} + \frac{1}{x - \tan 80^{\circ}} = 0.\]Enter the solutions, separated by commas. | Let $a = \tan 20^\circ,$ $b = \tan 40^\circ,$ and $c = \tan 80^\circ,$ so
\[\frac{1}{x - a} + \frac{1}{x + b} + \frac{1}{x - c} = 0.\]Then $(x + b)(x - c) + (x - a)(x - c) + (x - a)(x + b) = 0,$ which expands as
\[3x^2 + (-2a + 2b - 2c) x + (-ab + ac - bc) = 0.\]Let $t = \tan 10^\circ.$ Then from the addition formula for tangent,
\begin{align*}
-a + b - c &= -\tan 20^\circ + \tan 40^\circ - \tan 80^\circ \\
&= -\tan (30^\circ - 10^\circ) + \tan (30^\circ + \tan 10^\circ) - \frac{1}{\tan 10^\circ} \\
&= -\frac{\tan 30^\circ - \tan 10^\circ}{1 + \tan 30^\circ \tan 10^\circ} + \frac{\tan 30^\circ + \tan 10^\circ}{1 - \tan 30^\circ \tan 10^\circ} - \frac{1}{\tan 10^\circ} \\
&= -\frac{\frac{1}{\sqrt{3}} - t}{1 + \frac{t}{\sqrt{3}}} + \frac{\frac{1}{\sqrt{3}} + t}{1 - \frac{t}{\sqrt{3}}} - \frac{1}{t} \\
&= -\frac{1 - t \sqrt{3}}{\sqrt{3} + t} + \frac{1 + t \sqrt{3}}{\sqrt{3} - t} - \frac{1}{t} \\
&= -\frac{(1 - t \sqrt{3})(\sqrt{3} - t)}{3 - t^2} + \frac{(1 + t \sqrt{3})(\sqrt{3} + t)}{3 - t^2} - \frac{1}{t} \\
&= \frac{8t}{3 - t^2} - \frac{1}{t} \\
&= \frac{9t^2 - 3}{3t - t^3}.
\end{align*}By the triple angle formula,
\[\frac{1}{\sqrt{3}} = \tan 30^\circ = \tan (3 \cdot 10^\circ) = \frac{3t - t^3}{1 - 3t^2},\]so $\frac{1 - 3t^2}{3t - t^3} = \sqrt{3}.$ Then
\[\frac{9t^2 - 3}{3t - t^3} = -3 \sqrt{3},\]so $-2a + 2b - 2c = -6 \sqrt{3}.$
Also,
\begin{align*}
-ab + ac - bc &= -\tan 20^\circ \tan 40^\circ + \tan 20^\circ \tan 80^\circ - \tan 40^\circ \tan 80^\circ \\
&= -\frac{1 - t \sqrt{3}}{\sqrt{3} + t} \cdot \frac{1 + t \sqrt{3}}{\sqrt{3} - t} + \frac{1 - t \sqrt{3}}{\sqrt{3} + t} \cdot \frac{1}{t} - \frac{1 + t \sqrt{3}}{\sqrt{3} - t} \cdot \frac{1}{t} \\
&= -\frac{1 - 3t^2}{3 - t^2} + \frac{1}{t} \left( \frac{1 - t \sqrt{3}}{\sqrt{3} + t} - \frac{1 + t \sqrt{3}}{\sqrt{3} - t} \right) \\
&= -\frac{1 - 3t^2}{3 - t^2} + \frac{1}{t} \cdot \left( -\frac{8t}{3 - t^2} \right) \\
&= \frac{3t^2 - 1}{3 - t^2} - \frac{8}{3 - t^2} \\
&= \frac{3t^2 - 9}{3 - t^2} \\
&= -3.
\end{align*}Thus, the quadratic is
\[3x^2 - 6 \sqrt{3} x - 3 = 0.\]By the quadratic formula, the roots are $\boxed{2 + \sqrt{3}, -2 + \sqrt{3}}.$ | null | null | null | Level 5 | Precalculus | \(\boxed{None}\) | Find the solutions to
\[\frac{1}{x - \tan 20^{\circ}} + \frac{1}{x + \tan 40^{\circ}} + \frac{1}{x - \tan 80^{\circ}} = 0.\]Enter the solutions, separated by commas.
The following text is the beginning part of the answer, which you can refer to for solving the problem:
Let $a = \tan 20^\circ,$ $b = \tan 40^\circ,$ and $c = \tan 80^\circ,$ so
\[\frac{1}{x - a} + \frac{1}{x + b} + \frac{1}{x - c} = 0.\]Then $(x + b)(x - c) + (x - a)(x - c) + (x - a)(x + b) = 0,$ which expands as
\[3x^2 + (-2a + 2b - 2c) x + (-ab + ac - bc) = 0.\]Let $t = \tan 10^\circ.$ Then from the addition formula for tangent,
\begin{align*}
-a + b - c &= -\tan 20^\circ + \tan 40^\circ - \tan 80^\circ \\
&= -\tan (30^\circ - 10^\circ) + \tan (30^\circ + \tan 10^\circ) - \frac{1}{\tan 10^\circ} \\
&= -\frac{\tan 30^\circ - \tan 10^\circ}{1 + \tan 30^\circ \tan 10^\circ} + \frac{\tan 30^\circ + \tan 10^\circ}{1 - \tan 30^\circ \tan 10^\circ} - \frac{1}{\tan 10^\circ} \\
&= -\frac{\frac{1}{\sqrt{3}} - t}{1 + \frac{t}{\sqrt{3}}} + \frac{\frac{1}{\sqrt{3}} + t}{1 - \frac{t}{\sqrt{3}}} - \frac{1}{t} \\
&= -\frac{1 - t \sqrt{3}}{\sqrt{3} + t} + \frac{1 + t \sqrt{3}}{\sqrt{3} - t} - \frac{1}{t} \\
&= -\frac{(1 - t \sqrt{3})(\sqrt{3} - t)}{3 - t^2} + \frac{(1 + t \sqrt{3})(\sqrt{3} + t)}{3 - t^2} - \frac{1}{t} \\
&= \frac{8t}{3 - t^2} - \frac{1}{t} \\
&= \fr |
Let $\mathbf{v}$ and $\mathbf{w}$ be vectors such that $\|\mathbf{v}\| = 3$ and $\|\mathbf{w}\| = 4.$ Find the minimum value of $\mathbf{v} \cdot \mathbf{w}.$ | If $\theta$ is the angle between $\mathbf{v}$ and $\mathbf{w},$ then
\[\mathbf{v} \cdot \mathbf{w} = \|\mathbf{v}\| \|\mathbf{w}\| \cos \theta = 12 \cos \theta.\]This is minimized when $\cos \theta = -1,$ which gives us a minimum value of $\boxed{-12}.$ | null | null | null | Level 3 | Precalculus | \(\boxed{None}\) | Let $\mathbf{v}$ and $\mathbf{w}$ be vectors such that $\|\mathbf{v}\| = 3$ and $\|\mathbf{w}\| = 4.$ Find the minimum value of $\mathbf{v} \cdot \mathbf{w}.$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
If $\theta$ is the angle between $\mathbf{v}$ and $\mathbf{w},$ then
\[\mathbf{v} \cdot \mathbf{w} = \|\mathbf{v}\| \|\mathbf{ |
If $\sin x + \cos x = \frac{1}{5}$ and $0 < x < \pi,$ find $\tan x.$ | From the given equation, $\cos x = \frac{1}{5} - \sin x.$ Substituting into $\cos^2 x + \sin^2 x = 1,$ we get
\[\left( \frac{1}{5} - \sin x \right)^2 + \sin^2 x = 1.\]This simplifies to $25 \sin^2 x - 5 \sin x - 12 = 0,$ which factors as $(5 \sin x - 4)(5 \sin x + 3) = 0.$ Since $0 < x < \pi,$ $\sin x$ is positive, so $\sin x = \frac{4}{5}.$
Then $\cos x = \frac{1}{5} - \sin x = -\frac{3}{5},$ so
\[\tan x = \frac{\sin x}{\cos x} = \frac{-4/5}{3/5} = \boxed{-\frac{4}{3}}.\] | null | null | null | Level 5 | Precalculus | \(\boxed{None}\) | If $\sin x + \cos x = \frac{1}{5}$ and $0 < x < \pi,$ find $\tan x.$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
From the given equation, $\cos x = \frac{1}{5} - \sin x.$ Substituting into $\cos^2 x + \sin^2 x = 1,$ we get
\[\left( \frac{1}{5} - \sin x \right)^2 + \sin^2 x = 1.\]This simplifies to $25 \sin^2 x - 5 \sin x - 12 = 0,$ which factors as $ |
The matrix for projecting onto a certain plane $P,$ which passes through the origin, is given by
\[\renewcommand{\arraystretch}{1.5} \begin{pmatrix} \frac{13}{14} & -\frac{1}{7} & \frac{3}{14} \\ -\frac{1}{7} & \frac{5}{7} & \frac{3}{7} \\ \frac{3}{14} & \frac{3}{7} & \frac{5}{14} \end{pmatrix} \renewcommand{\arraystretch}{1}.\]Find the normal vector of plane $P.$ Enter your answer in the form $\begin{pmatrix} a \\ b \\ c \end{pmatrix},$ where $a,$ $b,$ and $c$ are integers, $a > 0,$ and $\gcd(|a|,|b|,|c|) = 1.$ | Since $\begin{pmatrix} a \\ b \\ c \end{pmatrix}$ is the normal vector, its projection is the zero vector. Thus,
\[\renewcommand{\arraystretch}{1.5} \begin{pmatrix} \frac{13}{14} & -\frac{1}{7} & \frac{3}{14} \\ -\frac{1}{7} & \frac{5}{7} & \frac{3}{7} \\ \frac{3}{14} & \frac{3}{7} & \frac{5}{14} \end{pmatrix} \renewcommand{\arraystretch}{1} \begin{pmatrix} a \\ b \\ c \end{pmatrix} = \begin{pmatrix} 0 \\ 0 \\ 0 \end{pmatrix}.\]Then $\frac{13}{14} a - \frac{1}{7} b + \frac{3}{14} = 0,$ $-\frac{1}{7} a + \frac{5}{7} b + \frac{3}{7} c = 0,$ and $\frac{3}{14} a + \frac{3}{7} b + \frac{5}{14} = 0.$ These reduce to
\begin{align*}
13a - 2b + 3c &= 0, \\
-a + 5b + 3c &= 0, \\
3a + 6b + 5c &= 0.
\end{align*}Subtracting the first two equations, we get $14a - 7b = 0,$ so $b = 2a.$ Then
\[-a + 10a + 3c = 0,\]so $c = -3a.$ Hence,
\[\begin{pmatrix} a \\ b \\ c \end{pmatrix} = \begin{pmatrix} a \\ 2a \\ -3a \end{pmatrix} = a \begin{pmatrix} 1 \\ 2 \\ -3 \end{pmatrix},\]so the vector we seek is $\boxed{\begin{pmatrix} 1 \\ 2 \\ -3 \end{pmatrix}}.$ | null | null | null | Level 5 | Precalculus | \(\boxed{None}\) | The matrix for projecting onto a certain plane $P,$ which passes through the origin, is given by
\[\renewcommand{\arraystretch}{1.5} \begin{pmatrix} \frac{13}{14} & -\frac{1}{7} & \frac{3}{14} \\ -\frac{1}{7} & \frac{5}{7} & \frac{3}{7} \\ \frac{3}{14} & \frac{3}{7} & \frac{5}{14} \end{pmatrix} \renewcommand{\arraystretch}{1}.\]Find the normal vector of plane $P.$ Enter your answer in the form $\begin{pmatrix} a \\ b \\ c \end{pmatrix},$ where $a,$ $b,$ and $c$ are integers, $a > 0,$ and $\gcd(|a|,|b|,|c|) = 1.$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
Since $\begin{pmatrix} a \\ b \\ c \end{pmatrix}$ is the normal vector, its projection is the zero vector. Thus,
\[\renewcommand{\arraystretch}{1.5} \begin{pmatrix} \frac{13}{14} & -\frac{1}{7} & \frac{3}{14} \\ -\frac{1}{7} & \frac{5}{7} & \frac{3}{7} \\ \frac{3}{14} & \frac{3}{7} & \frac{5}{14} \end{pmatrix} \renewcommand{\arraystretch}{1} \begin{pmatrix} a \\ b \\ c \end{pmatrix} = \begin{pmatrix} 0 \\ 0 \\ 0 \end{pmatrix}.\]Then $\frac{13}{14} a - \frac{1}{7} b + \frac{3}{14} = 0,$ $-\frac{1}{7} a + \frac{5}{7} b + |
Let $\mathbf{a},$ $\mathbf{b},$ and $\mathbf{c}$ be vectors such that $\|\mathbf{a}\| = 5,$ $\|\mathbf{b}\| = 7,$ and $\|\mathbf{c}\| = 9,$ and
\[\mathbf{a} + \mathbf{b} + \mathbf{c} = \mathbf{0}.\]Find $\mathbf{a} \cdot \mathbf{b} + \mathbf{a} \cdot \mathbf{c} + \mathbf{b} \cdot \mathbf{c}.$ | Since $\mathbf{a} + \mathbf{b} + \mathbf{c} = \mathbf{0},$
\[(\mathbf{a} + \mathbf{b} + \mathbf{c}) \cdot (\mathbf{a} + \mathbf{b} + \mathbf{c}) = 0.\]This expands as
\[\mathbf{a} \cdot \mathbf{a} + \mathbf{b} \cdot \mathbf{b} + \mathbf{c} \cdot \mathbf{c} + 2 \mathbf{a} \cdot \mathbf{b} + 2 \mathbf{a} \cdot \mathbf{c} + 2 \mathbf{b} \cdot \mathbf{c} = 0.\]Since $\mathbf{a} \cdot \mathbf{a} = \|\mathbf{a}\|^2 = 25,$ $\mathbf{b} \cdot \mathbf{b} = \|\mathbf{b}\|^2 = 49,$ and $\mathbf{c} \cdot \mathbf{c} = \|\mathbf{c}\|^2 = 81,$
\[2(\mathbf{a} \cdot \mathbf{b} + \mathbf{a} \cdot \mathbf{c} + \mathbf{b} \cdot \mathbf{c}) + 155 = 0.\]Hence, $\mathbf{a} \cdot \mathbf{b} + \mathbf{a} \cdot \mathbf{c} + \mathbf{b} \cdot \mathbf{c} = \boxed{-\frac{155}{2}}.$ | null | null | null | Level 4 | Precalculus | \(\boxed{None}\) | Let $\mathbf{a},$ $\mathbf{b},$ and $\mathbf{c}$ be vectors such that $\|\mathbf{a}\| = 5,$ $\|\mathbf{b}\| = 7,$ and $\|\mathbf{c}\| = 9,$ and
\[\mathbf{a} + \mathbf{b} + \mathbf{c} = \mathbf{0}.\]Find $\mathbf{a} \cdot \mathbf{b} + \mathbf{a} \cdot \mathbf{c} + \mathbf{b} \cdot \mathbf{c}.$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
Since $\mathbf{a} + \mathbf{b} + \mathbf{c} = \mathbf{0},$
\[(\mathbf{a} + \mathbf{b} + \mathbf{c}) \cdot (\mathbf{a} + \mathbf{b} + \mathbf{c}) = 0.\]This expands as
\[\mathbf{a} \cdot \mathbf{a} + \mathbf{b} \cdot \mathbf{b} + \mathbf{c} \cdot \mathbf{c} + 2 \mathbf{a} \cdot \mathbf{b} + 2 \mathbf{a} \cdot \mathbf{c} + 2 \mathbf{b} \cdot \mathbf{c} = 0.\]Since $\mathbf{a} \cd |
Find the smallest positive integer solution to $\tan{19x^{\circ}}=\dfrac{\cos{96^{\circ}}+\sin{96^{\circ}}}{\cos{96^{\circ}}-\sin{96^{\circ}}}$. | By the tangent addition formula,
\begin{align*}
\frac{\cos 96^\circ + \sin 96^\circ}{\cos 96^\circ - \sin 96^\circ} &= \frac{1 + \tan 96^\circ}{1 - \tan 96^\circ} \\
&= \frac{\tan 45^\circ + \tan 96^\circ}{1 - \tan 45^\circ \tan 96^\circ} \\
&= \tan (45^\circ + 96^\circ) \\
&= \tan 141^\circ.
\end{align*}Thus, we seek the smallest positive integer solution to
\[\tan 19x^\circ = \tan 141^\circ.\]This means $19x - 141 = 180n$ for some integer $n,$ or $19x - 180n = 141.$ We can use the Extended Euclidean Algorithm to find the smallest positive integer solution.
Running the Euclidean Algorithm on 180 and 19, we get
\begin{align*}
180 &= 9 \cdot 19 + 9, \\
19 &= 2 \cdot 9 + 1, \\
9 &= 9 \cdot 1.
\end{align*}Then
\begin{align*}
1 &= 19 - 2 \cdot 9 \\
&= 19 - 2 \cdot (180 - 9 \cdot 19) \\
&= 19 \cdot 19 - 2 \cdot 180.
\end{align*}Multiplying both sides by 141, we get
\[2679 \cdot 19 - 282 \cdot 180 = 141.\]Note that if $(x,n)$ is a solution to $19x - 180n = 141,$ then so is $(x - 180,n + 19).$ Thus, we reduce 2679 modulo 180, to get $x = \boxed{159}.$
Alternatively, we want to solve
\[19x \equiv 141 \pmod{180}.\]Multiplying both sides by 19, we get
\[361x \equiv 2679 \pmod{180},\]which reduces to $x \equiv \boxed{159} \pmod{180}.$ | null | null | null | Level 5 | Precalculus | \(\boxed{None}\) | Find the smallest positive integer solution to $\tan{19x^{\circ}}=\dfrac{\cos{96^{\circ}}+\sin{96^{\circ}}}{\cos{96^{\circ}}-\sin{96^{\circ}}}$.
The following text is the beginning part of the answer, which you can refer to for solving the problem:
By the tangent addition formula,
\begin{align*}
\frac{\cos 96^\circ + \sin 96^\circ}{\cos 96^\circ - \sin 96^\circ} &= \frac{1 + \tan 96^\circ}{1 - \tan 96^\circ} \\
&= \frac{\tan 45^\circ + \tan 96^\circ}{1 - \tan 45^\circ \tan 96^\circ} \\
&= \tan (45^\circ + 96^\circ) \\
&= \tan 141^\circ.
\end{align*}Thus, we seek the smallest positive integer solution to
\[\tan 19x^\circ = \tan 141^\circ.\]This means $19x - 141 = 180n$ for some integer $n,$ or $19x - 180n = 141.$ We can use the Extended Euclidean Algorithm to find the smallest positive integer solution.
Running the Euclidean Algorithm on 180 and 19, we get
\be |
The matrix for reflecting over a certain line $\ell,$ which passes through the origin, is given by
\[\renewcommand{\arraystretch}{1.5} \begin{pmatrix} -\frac{2}{3} & -\frac{2}{3} & -\frac{1}{3} \\ -\frac{2}{3} & \frac{1}{3} & \frac{2}{3} \\ -\frac{1}{3} & \frac{2}{3} & -\frac{2}{3} \end{pmatrix} \renewcommand{\arraystretch}{1}.\]Find the direction vector of line $\ell.$ Enter your answer in the form $\begin{pmatrix} a \\ b \\ c \end{pmatrix},$ where $a,$ $b,$ and $c$ are integers, $a > 0,$ and $\gcd(|a|,|b|,|c|) = 1.$ | Since $\begin{pmatrix} a \\ b \\ c \end{pmatrix}$ actually lies on $\ell,$ the reflection takes this vector to itself. Then
\[\renewcommand{\arraystretch}{1.5} \begin{pmatrix} -\frac{2}{3} & -\frac{2}{3} & -\frac{1}{3} \\ -\frac{2}{3} & \frac{1}{3} & \frac{2}{3} \\ -\frac{1}{3} & \frac{2}{3} & -\frac{2}{3} \end{pmatrix} \renewcommand{\arraystretch}{1} \begin{pmatrix} a \\ b \\ c \end{pmatrix} = \begin{pmatrix} a \\ b \\ c \end{pmatrix}.\]This gives us
\[\renewcommand{\arraystretch}{1.5} \begin{pmatrix} -\frac{2}{3} a - \frac{2}{3} b - \frac{1}{3} c \\ -\frac{2}{3} a + \frac{1}{3} b + \frac{2}{3} c \\ -\frac{1}{3} a + \frac{2}{3} b - \frac{2}{3} c \end{pmatrix} \renewcommand{\arraystretch}{1} = \begin{pmatrix} a \\ b \\ c \end{pmatrix}.\]Then $-\frac{2}{3} a - \frac{2}{3} b - \frac{1}{3} c = a,$ $-\frac{2}{3} a + \frac{1}{3} b + \frac{2}{3} c = b,$ and $-\frac{1}{3} a + \frac{2}{3} b - \frac{2}{3} c = c.$ These reduce to
\begin{align*}
5a + 2b + c &= 0, \\
a + b - c &= 0, \\
a - 2b + 5c &= 0.
\end{align*}Adding the first two equations, we get $6a + 3b = 0,$ so $b = -2a.$ Then
\[a - 2a - c = 0,\]so $c = -a.$ (And if $b = -2a$ and $c = -a,$ then the third equation $a - 2b + 5c = 0$ is satisfied.) Hence,
\[\begin{pmatrix} a \\ b \\ c \end{pmatrix} = \begin{pmatrix} a \\ -2a \\ -a \end{pmatrix} = a \begin{pmatrix} 1 \\ -2 \\ -1 \end{pmatrix}.\]Thus, the vector we seek is $\boxed{\begin{pmatrix} 1 \\ -2 \\ -1 \end{pmatrix}}.$ | null | null | null | Level 5 | Precalculus | \(\boxed{None}\) | The matrix for reflecting over a certain line $\ell,$ which passes through the origin, is given by
\[\renewcommand{\arraystretch}{1.5} \begin{pmatrix} -\frac{2}{3} & -\frac{2}{3} & -\frac{1}{3} \\ -\frac{2}{3} & \frac{1}{3} & \frac{2}{3} \\ -\frac{1}{3} & \frac{2}{3} & -\frac{2}{3} \end{pmatrix} \renewcommand{\arraystretch}{1}.\]Find the direction vector of line $\ell.$ Enter your answer in the form $\begin{pmatrix} a \\ b \\ c \end{pmatrix},$ where $a,$ $b,$ and $c$ are integers, $a > 0,$ and $\gcd(|a|,|b|,|c|) = 1.$
The following text is the beginning part of the answer, which you can refer to for solving the problem:
Since $\begin{pmatrix} a \\ b \\ c \end{pmatrix}$ actually lies on $\ell,$ the reflection takes this vector to itself. Then
\[\renewcommand{\arraystretch}{1.5} \begin{pmatrix} -\frac{2}{3} & -\frac{2}{3} & -\frac{1}{3} \\ -\frac{2}{3} & \frac{1}{3} & \frac{2}{3} \\ -\frac{1}{3} & \frac{2}{3} & -\frac{2}{3} \end{pmatrix} \renewcommand{\arraystretch}{1} \begin{pmatrix} a \\ b \\ c \end{pmatrix} = \begin{pmatrix} a \\ b \\ c \end{pmatrix}.\]This gives us
\[\renewcommand{\arraystretch}{1.5} \begin{pmatrix} -\frac{2}{3} a - \frac{2}{3} b - \frac{1}{3} c \\ -\frac{2}{3} a + \frac{1}{3} b + \frac{2}{3} c \\ -\frac{1}{3} a + \frac{2}{3} b - \frac{2}{3} c \end{pmatrix} \renewcommand{\arraystretch}{1} = \begin{pmatrix} a \\ |
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