Multivariable Calculus : Multivariable Calculus

Study concepts, example questions & explanations for Multivariable Calculus

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14 Practice Tests Question of the Day Flashcards Learn by Concept

Example Questions

Example Question #1 : Arc Length

Determine the length of the curve \(\displaystyle \vec{r}(t)=\left \langle t,4\sin(2t),4\cos(2t)\right \rangle\), on the interval \(\displaystyle 0\leq t\leq 2\pi\).

Possible Answers:

\(\displaystyle 1\)

\(\displaystyle \sqrt{65}\)

\(\displaystyle 2\pi\sqrt{65}\)

\(\displaystyle \pi\)

\(\displaystyle 2\pi\)

Correct answer:

\(\displaystyle 2\pi\sqrt{65}\)

Explanation:

First we need to find the tangent vector, and find its magnitude.

\(\displaystyle \vec{v}(t)=\vec{r}\ '(t)=\left \langle 1, 8\cos(2t), -8\sin(2t)\right \rangle\)

\(\displaystyle \left \| \vec{v}(t)\right \|=\sqrt{1^2+(8\cos(2t))^2+(-8\sin(2t))^2}\)

\(\displaystyle \left \| \vec{v}(t)\right \|=\sqrt{1+64\cos^2(2t)+64\sin^2(2t)}\)

\(\displaystyle \left \| \vec{v}(t)\right \|=\sqrt{1+64(\cos^2(2t)+\sin^2(2t))}\)

\(\displaystyle \left \| \vec{v}(t)\right \|=\sqrt{1+64}=\sqrt{65}\)

 

Now we can set up our arc length integral

 

\(\displaystyle L=\int_{a}^{b}\left \| \vec{v}(t)\right \|dt\)

 

\(\displaystyle L=\int_{0}^{2\pi} \sqrt{65}\ dt=t\sqrt{65}\Big|_{0}^{2\pi}=2\pi\sqrt{65}\)

Example Question #1 : Change Of Variables

Convert the following into spherical coordinates.

\(\displaystyle x=\sin(t)\)

\(\displaystyle y=\cos(t)\)

\(\displaystyle z=1\)

Possible Answers:

\(\displaystyle \rho=\sqrt{2}\)

\(\displaystyle \phi=\frac{\pi}{4}\)

\(\displaystyle \theta=\tan^{-1}(\cot(t))\)

\(\displaystyle \rho=1\)

\(\displaystyle \phi=\frac{\pi}{2}\)

\(\displaystyle \theta=\tan(\cot(t))\)

\(\displaystyle \rho=\sqrt{2}\)

\(\displaystyle \phi=0\)

\(\displaystyle \theta=\tan(\cot(t))\)

\(\displaystyle \rho=\sqrt{2}\)

\(\displaystyle \phi=\frac{\pi}{4}\)

\(\displaystyle \theta=\tan^{-1}(\cot(t))\)

\(\displaystyle \rho=2\)

\(\displaystyle \phi=-\frac{\pi}{4}\)

\(\displaystyle \theta=\tan^{-1}(\cot(t))\)

Correct answer:

\(\displaystyle \rho=\sqrt{2}\)

\(\displaystyle \phi=\frac{\pi}{4}\)

\(\displaystyle \theta=\tan^{-1}(\cot(t))\)

Explanation:

In order to convert to spherical coordinates , we need to remember the conversion equations.

\(\displaystyle \rho=\sqrt{x^2+y^2+z^2}\)

\(\displaystyle \theta=\tan^{-1}\Big(\frac{y}{x}\Big)\)

\(\displaystyle \phi=\tan^{-1}\Big(\frac{\sqrt{x^2+y^2}}{z}\Big)\)

Now lets apply this to our problem.

\(\displaystyle \rho=\sqrt{(\sin(t))^2+(\cos(t))^2+1^2}=\sqrt{1+1}=\sqrt{2}\)

\(\displaystyle \phi=\tan^{-1}\Big(\frac{\sqrt{(\sin{t})^2+(\cos{t})^2}}{1}\Big)=\tan^{-1}(1)=\frac{\pi}{4}\)

\(\displaystyle \theta=\tan^{-1}\Big(\frac{\cos(t)}{\sin(t)}\Big)=\tan^{-1}(\cot(t))\)

Example Question #1 : Change Of Variables

Evaluate \(\displaystyle \int \int_R 3x+2y \ dA\), where \(\displaystyle R\) is the trapezoidal region with vertices given by \(\displaystyle (0,0)\)\(\displaystyle (5,0)\)\(\displaystyle (\frac{5}{2}, \frac{5}{2})\), and \(\displaystyle (\frac{5}{2}, -\frac{5}{2})\),

using the transformation \(\displaystyle x=2u+3v\), and \(\displaystyle y=2u-3v\).

Possible Answers:

\(\displaystyle \frac{375}{2}\)

\(\displaystyle \frac{37}{4}\)

\(\displaystyle \frac{375}{4}\)

\(\displaystyle \frac{35}{4}\)

\(\displaystyle 0\)

Correct answer:

\(\displaystyle \frac{375}{4}\)

Explanation:

The first thing we have to do is figure out the general equations for the lines that create the trapezoid.

 

\(\displaystyle y=x\)

\(\displaystyle y=-x\)

\(\displaystyle y=-x+5\)

\(\displaystyle y=x-5\)

 

Now we have the general equations for out trapezoid, now we need to plug in our transformations into these equations.

\(\displaystyle y=x\)

\(\displaystyle 2u+3v=2u-3v\)

\(\displaystyle -6v=0\rightarrow v=0\)

 

\(\displaystyle y=-x\)

\(\displaystyle 2u+3v=-2u+3v\)

\(\displaystyle 4u=0\rightarrow u=0\)

 

\(\displaystyle y=-x+5\)

\(\displaystyle 2u+3v=-2u+3v+5\)

\(\displaystyle 4u=5\rightarrow u=\frac{5}{4}\)

\(\displaystyle y=x-5\)

\(\displaystyle 2u+3v=2u-3v-5\)

\(\displaystyle -6v=-5\rightarrow v=\frac{5}{6}\)

So our region is a rectangle given by \(\displaystyle 0 \leq u \leq \frac{5}{4}\)\(\displaystyle 0 \leq v \leq \frac{5}{6}\)

 

Next we need to calculate the Jacobian.

 

\(\displaystyle \begin{vmatrix} 2 & 3\\ 2 & -3 \end{vmatrix} =-6-6=-12\)

 

Now we can put the integral together.

 

\(\displaystyle \int_{0}^{\frac{5}{6}} \int_{0}^{\frac{5}{4}} (3(2u+3v)+2(2u-3v))) \cdot \left | -12\right | \ du\ dv\)

 

\(\displaystyle =\int_{0}^{\frac{5}{6}} \int_{0}^{\frac{5}{4}} 120u+36v \ du\ dv\)

\(\displaystyle =\int_{0}^{\frac{5}{6}} 60u^2+36uv \Big|_{0}^{\frac{5}{4}}\ dv\)

\(\displaystyle =\int_{0}^{\frac{5}{6}} 60( \frac{5}{4})^2+36(\frac{5}{4})v-0 \ dv\)

\(\displaystyle =\int_{0}^{\frac{5}{6}} \frac{375}{4}+45v \ dv\)

\(\displaystyle =\frac{375}{4}v+\frac{45}{2}v^2\Big|_{0}^{\frac{5}{6}} \ dv\)

\(\displaystyle =\frac{375}{4}\cdot\frac{5}{6}+\frac{45}{2}\cdot\Big(\frac{5}{6}\Big)^2 -0=\frac{375}{4}\)

Example Question #1 : Double Integrations On Plane

Convert the following into spherical coordinates.

\(\displaystyle x=\sin(t)\)

\(\displaystyle y=\cos(t)\)

\(\displaystyle z=1\)

Possible Answers:

 

\(\displaystyle \rho=\sqrt{2}\)
\(\displaystyle \phi=\frac{\pi}{4}\)
\(\displaystyle \theta=\tan^{-1}(\cot(t))\)

\(\displaystyle \rho=2\)
\(\displaystyle \phi=-\frac{\pi}{4}\)
\(\displaystyle \theta=\tan^{-1}(\cot(t))\)

\(\displaystyle \rho=1\)
\(\displaystyle \phi=\frac{\pi}{2}\)
\(\displaystyle \theta=\tan(\cot(t))\)

\(\displaystyle \rho=\sqrt{2}\)
\(\displaystyle \phi=0\)
\(\displaystyle \theta=\tan(\cot(t))\)

\(\displaystyle \rho=\sqrt{2}\)
\(\displaystyle \phi=-\frac{\pi}{4}\)
\(\displaystyle \theta=\tan^{-1}(\cot(t))\)

Correct answer:

 

\(\displaystyle \rho=\sqrt{2}\)
\(\displaystyle \phi=\frac{\pi}{4}\)
\(\displaystyle \theta=\tan^{-1}(\cot(t))\)

Explanation:

In order to convert to spherical coordinates , we need to remember the conversion equations.

\(\displaystyle \rho=\sqrt{x^2+y^2+z^2}\)

\(\displaystyle \theta=\tan^{-1}\Big(\frac{y}{x}\Big)\)

\(\displaystyle \phi=\tan^{-1}\Big(\frac{\sqrt{x^2+y^2}}{z}\Big)\)

Now lets apply this to our problem.

\(\displaystyle \rho=\sqrt{(\sin(t))^2+(\cos(t))^2+1^2}=\sqrt{1+1}=\sqrt{2}\)

\(\displaystyle \phi=\tan^{-1}\Big(\frac{\sqrt{(\sin{t})^2+(\cos{t})^2}}{1}\Big)=\tan^{-1}(1)=\frac{\pi}{4}\)

\(\displaystyle \theta=\tan^{-1}\Big(\frac{\cos(t)}{\sin(t)}\Big)=\tan^{-1}(\cot(t))\)

Example Question #1 : Divergence, Gradient, & Curl

Calculate the curl for the following vector field.

\(\displaystyle \vec{F}=x^3y^2\ \vec{i}+x^2y^3z^4\ \vec{j}+x^2z^2\ \vec{k}\)

Possible Answers:

\(\displaystyle curl\ \vec{F}=\Big(2x^2z^3\Big)\vec{i}-\Big(2yz^2\Big)\vec{j}-\Big(-2x^3y\Big)\vec{k}\)

\(\displaystyle curl\ \vec{F}=\Big(4x^2y^3z^3\Big)\vec{i}+\Big(2xz^2\Big)\vec{j}+\Big(-2xy^3z^4+2x^3y\Big)\vec{k}\)

\(\displaystyle curl\ \vec{F}=\Big(2x^2z^3\Big)\vec{i}+\Big(2yz^2\Big)\vec{j}+\Big(-2x^3y\Big)\vec{k}\)

\(\displaystyle curl\ \vec{F}=\Big(-4x^2y^3z^3\Big)\vec{i}+\Big(-2xz^2\Big)\vec{j}+\Big(2xy^3z^4-2x^3y\Big)\vec{k}\)

\(\displaystyle curl\ \vec{F}=0\)

Correct answer:

\(\displaystyle curl\ \vec{F}=\Big(-4x^2y^3z^3\Big)\vec{i}+\Big(-2xz^2\Big)\vec{j}+\Big(2xy^3z^4-2x^3y\Big)\vec{k}\)

Explanation:

In order to calculate the curl, we need to recall the formula.

\(\displaystyle \\curl\ \vec{F}=\triangledown \times \vec{F}=\begin{vmatrix} \vec{i} & \vec{j} & \vec{k}\\ \frac{\partial}{\partial x}& \frac{\partial}{\partial y} & \frac{\partial}{\partial z} \\ P & Q & R \end{vmatrix}\\ \\ \\ =\Big(\frac{\partial R}{\partial y}-\frac{\partial Q}{\partial z}\ \Big)\vec{i}+\Big(\frac{\partial P}{\partial z}-\frac{\partial R}{\partial x}\ \Big)\vec{j}+\Big(\frac{\partial Q}{\partial x}-\frac{\partial P}{\partial y}\ \Big)\vec{k}\)

where \(\displaystyle P\)\(\displaystyle Q\), and \(\displaystyle R\) correspond to the components of a given vector field: \(\displaystyle \vec{F}=P\vec{i}+Q\vec{j}+R\vec{k}\)

 

Now lets apply this to out situation.

 

\(\displaystyle curl\ \vec{F}=\triangledown \times \vec{F}=\begin{vmatrix} \vec{i} & \vec{j} & \vec{k}\\\\ \frac{\partial}{\partial x}& \frac{\partial}{\partial y} & \frac{\partial}{\partial z} \\\\ x^3y^2 & x^2y^3z^4 & x^2z^2 \end{vmatrix}\)

 

\(\displaystyle \\=\Big(\frac{\partial }{\partial y}\Big(x^2z^2\Big)-\frac{\partial}{\partial z}\Big(x^2y^3z^4\Big)\ \Big)\vec{i}+\Big(\frac{\partial}{\partial z}\Big(x^3y^2\Big)-\frac{\partial}{\partial x}\Big(x^2z^2\Big)\ \Big)\vec{j}+\Big(\frac{\partial}{\partial x}\Big(x^2y^3z^4\Big)-\frac{\partial}{\partial y}\Big(x^3y^2\Big)\ \Big)\vec{k}\)

 

\(\displaystyle =\Big(0-4x^2y^3z^3\Big)\vec{i}+\Big(0-2xz^2\Big)\vec{j}+\Big(2xy^3z^4-2x^3y\Big)\vec{k}\)

Thus the curl is

\(\displaystyle =\Big(-4x^2y^3z^3\Big)\vec{i}+\Big(-2xz^2\Big)\vec{j}+\Big(2xy^3z^4-2x^3y\Big)\vec{k}\)

Example Question #1 : Divergence, Gradient, & Curl

Compute \(\displaystyle div\vec{F}\), where \(\displaystyle \vec{F}=10x^2\ln(yz)\vec{i}+xyz\vec{j}+xz\ln(y)\vec{k}\).

Possible Answers:

\(\displaystyle div\vec{F}=20x\ln(yz)+xz+x\ln(y)\)

\(\displaystyle div\vec{F}=20x\ln(z)+yz+x\ln(y)\)

\(\displaystyle div\vec{F}=0\)

\(\displaystyle div\vec{F}=20x\ln(yz)-xz-x\ln(y)\)

\(\displaystyle div\vec{F}=20x\ln(yz)-xz+x\ln(y)\)

Correct answer:

\(\displaystyle div\vec{F}=20x\ln(yz)+xz+x\ln(y)\)

Explanation:

All we need to do is calculate the partial derivatives and add them together.

\(\displaystyle div\vec{F}=\frac{\partial}{\partial x}(10x^2\ln(yz))+\frac{\partial}{\partial y}(xyz)+\frac{\partial}{\partial z}(xz\ln(y))\)

\(\displaystyle div\vec{F}=20x\ln(yz)+xz+x\ln(y)\)

Example Question #1 : Divergence, Gradient, & Curl

Calculate the curl for the following vector field.

\(\displaystyle \vec{F}=x^3y^2\ \vec{i}+x^2y^3z^4\ \vec{j}+x^2z^2\ \vec{k}\)

Possible Answers:

\(\displaystyle curl\ \vec{F}=\Big(-4x^2y^3z^3\Big)\vec{i}+\Big(-2xz^2\Big)\vec{j}+\Big(2xy^3z^4-2x^3y\Big)\vec{k}\)

\(\displaystyle curl\ \vec{F}=\Big(4x^2y^3z^3\Big)\vec{i}+\Big(2xz^2\Big)\vec{j}+\Big(-2xy^3z^4+2x^3y\Big)\vec{k}\)

\(\displaystyle curl\ \vec{F}=\Big(2x^2z^3\Big)\vec{i}-\Big(2yz^2\Big)\vec{j}-\Big(-2x^3y\Big)\vec{k}\)

\(\displaystyle curl\ \vec{F}=\Big(2x^2z^3\Big)\vec{i}+\Big(2yz^2\Big)\vec{j}+\Big(-2x^3y\Big)\vec{k}\)

\(\displaystyle curl\ \vec{F}=0\)

Correct answer:

\(\displaystyle curl\ \vec{F}=\Big(-4x^2y^3z^3\Big)\vec{i}+\Big(-2xz^2\Big)\vec{j}+\Big(2xy^3z^4-2x^3y\Big)\vec{k}\)

Explanation:

In order to calculate the curl, we need to recall the formula.

\(\displaystyle \\curl\ \vec{F}=\triangledown \times \vec{F}=\begin{vmatrix} \vec{i} & \vec{j} & \vec{k}\\ \frac{\partial}{\partial x}& \frac{\partial}{\partial y} & \frac{\partial}{\partial z} \\ P & Q & R \end{vmatrix}\\ \\ \\ =\Big(\frac{\partial R}{\partial y}-\frac{\partial Q}{\partial z}\ \Big)\vec{i}+\Big(\frac{\partial P}{\partial z}-\frac{\partial R}{\partial x}\ \Big)\vec{j}+\Big(\frac{\partial Q}{\partial x}-\frac{\partial P}{\partial y}\ \Big)\vec{k}\)

where \(\displaystyle P\)\(\displaystyle Q\), and \(\displaystyle R\) correspond to the components of a given vector field: \(\displaystyle \vec{F}=P\vec{i}+Q\vec{j}+R\vec{k}\)

 

Now lets apply this to out situation.

 

\(\displaystyle curl\ \vec{F}=\triangledown \times \vec{F}=\begin{vmatrix} \vec{i} & \vec{j} & \vec{k}\\\\ \frac{\partial}{\partial x}& \frac{\partial}{\partial y} & \frac{\partial}{\partial z} \\\\ x^3y^2 & x^2y^3z^4 & x^2z^2 \end{vmatrix}\)

 

\(\displaystyle \\=\Big(\frac{\partial }{\partial y}\Big(x^2z^2\Big)-\frac{\partial}{\partial z}\Big(x^2y^3z^4\Big)\ \Big)\vec{i}+\Big(\frac{\partial}{\partial z}\Big(x^3y^2\Big)-\frac{\partial}{\partial x}\Big(x^2z^2\Big)\ \Big)\vec{j}+\Big(\frac{\partial}{\partial x}\Big(x^2y^3z^4\Big)-\frac{\partial}{\partial y}\Big(x^3y^2\Big)\ \Big)\vec{k}\)

 

\(\displaystyle =\Big(0-4x^2y^3z^3\Big)\vec{i}+\Big(0-2xz^2\Big)\vec{j}+\Big(2xy^3z^4-2x^3y\Big)\vec{k}\)

Thus the curl is

\(\displaystyle =\Big(-4x^2y^3z^3\Big)\vec{i}+\Big(-2xz^2\Big)\vec{j}+\Big(2xy^3z^4-2x^3y\Big)\vec{k}\)

Example Question #2 : Divergence, Gradient, & Curl

Compute \(\displaystyle div\vec{F}\), where \(\displaystyle \vec{F}=10x^2\ln(yz)\vec{i}+xyz\vec{j}+xz\ln(y)\vec{k}\).

Possible Answers:

\(\displaystyle div\vec{F}=0\)

\(\displaystyle div\vec{F}=20x\ln(yz)-xz+x\ln(y)\)

\(\displaystyle div\vec{F}=20x\ln(z)+yz+x\ln(y)\)

\(\displaystyle div\vec{F}=20x\ln(yz)-xz-x\ln(y)\)

\(\displaystyle div\vec{F}=20x\ln(yz)+xz+x\ln(y)\)

Correct answer:

\(\displaystyle div\vec{F}=20x\ln(yz)+xz+x\ln(y)\)

Explanation:

All we need to do is calculate the partial derivatives and add them together.

\(\displaystyle div\vec{F}=\frac{\partial}{\partial x}(10x^2\ln(yz))+\frac{\partial}{\partial y}(xyz)+\frac{\partial}{\partial z}(xz\ln(y))\)

\(\displaystyle div\vec{F}=20x\ln(yz)+xz+x\ln(y)\)

Example Question #1 : Triple Integration Of Surface

Evaluate \(\displaystyle \int \int \int_D y \ dV\), where \(\displaystyle D\) is the region below the plane \(\displaystyle z=x+1\) , above the \(\displaystyle xy\) plane and between the cylinders \(\displaystyle x^2+y^2=1\), and \(\displaystyle x^2+y^2=9\).

Possible Answers:

\(\displaystyle \frac{\pi}{4}\)

\(\displaystyle \pi\)

\(\displaystyle 0\)

\(\displaystyle \frac{\pi}{2}\)

\(\displaystyle 2 \pi\)

Correct answer:

\(\displaystyle 0\)

Explanation:

We need to figure out our boundaries for our integral.

We need to convert everything into cylindrical coordinates. Remeber we are above the \(\displaystyle xy\) plane, this means we are above \(\displaystyle z=0\).

\(\displaystyle 0\leq z \leq x+1 \rightarrow 0\leq z \leq r\cos(\theta)+1\)

The region \(\displaystyle D\) is between two circles \(\displaystyle x^2+y^2=1\), and \(\displaystyle x^2+y^2=9\).

This means that 

\(\displaystyle 0 \leq \theta \leq 2\pi\)

\(\displaystyle 1\leq r \leq 3\)

\(\displaystyle \int \int \int_D y \ dV=\int_{0}^{2\pi} \int_{1}^{3} \int_{0}^{r\cos(\theta)+1} r\sin(\theta) r\ dz \ dr \ d\theta\)

\(\displaystyle =\int_{0}^{2\pi} \int_{1}^{3} \int_{0}^{r\cos(\theta)+1} r^2\sin(\theta) \ dz \ dr \ d\theta\)

\(\displaystyle =\int_{0}^{2\pi} \int_{1}^{3} zr^2\sin(\theta) \Big|_{0}^{r\cos(\theta)+1} \ dr \ d\theta\)

\(\displaystyle =\int_{0}^{2\pi} \int_{1}^{3} (r\cos(\theta)+1)r^2\sin(\theta)-0 \ dr \ d\theta\)

\(\displaystyle =\int_{0}^{2\pi} \int_{1}^{3} r^3\sin(\theta)\cos(\theta)+r^2\sin(\theta) \ dr \ d\theta\)

\(\displaystyle =\int_{0}^{2\pi} \frac{1}{4}r^4\sin(\theta)\cos(\theta)+\frac{1}{3}r^3\sin(\theta) \Big|_{1}^{3}\ d\theta\)

\(\displaystyle =\int_{0}^{2\pi} (\frac{1}{4}(3)^4\sin(\theta)\cos(\theta)+\frac{1}{3}(3)^3\sin(\theta))-(\frac{1}{4}(1)^4\sin(\theta)\cos(\theta)+\frac{1}{3}(1)^3\sin(\theta)) \ d\theta\)

\(\displaystyle =\int_{0}^{2\pi} (\frac{81}{4}\sin(\theta)\cos(\theta)+9\sin(\theta))-(\frac{1}{4}\sin(\theta)\cos(\theta)+\frac{1}{3}\sin(\theta)) \ d\theta\)

\(\displaystyle =\int_{0}^{2\pi} 20\sin(\theta)\cos(\theta)+\frac{26}{3}\sin(\theta) \ d\theta\)

\(\displaystyle = -\frac{1}{2}\cdot20\cos^2(\theta)-\frac{26}{3}\cos(\theta)\Big|_{0}^{2\pi}\)

\(\displaystyle = -\frac{1}{2}\cdot20\cos^2(2\pi)-\frac{26}{3}\cos(2\pi)-(-\frac{1}{2}\cdot20\cos^2(0)-\frac{26}{3}\cos(0))\)

\(\displaystyle = -\frac{1}{2}\cdot20(1)-\frac{26}{3}(1)-(-\frac{1}{2}\cdot20(1)-\frac{26}{3}(1))\)

\(\displaystyle = -10-\frac{26}{3}-(-10-\frac{26}{3})=0\)

 

Example Question #1 : Parameterization & Surface Integrals

Evaluate \(\displaystyle \int \int \int_D y \ dV\), where \(\displaystyle D\) is the region below the plane \(\displaystyle z=x+1\) , above the \(\displaystyle xy\) plane and between the cylinders \(\displaystyle x^2+y^2=1\), and \(\displaystyle x^2+y^2=9\).

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle 2 \pi\)

\(\displaystyle \frac{\pi}{2}\)

\(\displaystyle \frac{\pi}{4}\)

\(\displaystyle \pi\)

Correct answer:

\(\displaystyle 0\)

Explanation:

We need to figure out our boundaries for our integral.

We need to convert everything into cylindrical coordinates. Remeber we are above the \(\displaystyle xy\) plane, this means we are above \(\displaystyle z=0\).

\(\displaystyle 0\leq z \leq x+1 \rightarrow 0\leq z \leq r\cos(\theta)+1\)

The region \(\displaystyle D\) is between two circles \(\displaystyle x^2+y^2=1\), and \(\displaystyle x^2+y^2=9\).

This means that 

\(\displaystyle 0 \leq \theta \leq 2\pi\)

\(\displaystyle 1\leq r \leq 3\)

\(\displaystyle \int \int \int_D y \ dV=\int_{0}^{2\pi} \int_{1}^{3} \int_{0}^{r\cos(\theta)+1} r\sin(\theta) r\ dz \ dr \ d\theta\)

\(\displaystyle =\int_{0}^{2\pi} \int_{1}^{3} \int_{0}^{r\cos(\theta)+1} r^2\sin(\theta) \ dz \ dr \ d\theta\)

\(\displaystyle =\int_{0}^{2\pi} \int_{1}^{3} zr^2\sin(\theta) \Big|_{0}^{r\cos(\theta)+1} \ dr \ d\theta\)

\(\displaystyle =\int_{0}^{2\pi} \int_{1}^{3} (r\cos(\theta)+1)r^2\sin(\theta)-0 \ dr \ d\theta\)

\(\displaystyle =\int_{0}^{2\pi} \int_{1}^{3} r^3\sin(\theta)\cos(\theta)+r^2\sin(\theta) \ dr \ d\theta\)

\(\displaystyle =\int_{0}^{2\pi} \frac{1}{4}r^4\sin(\theta)\cos(\theta)+\frac{1}{3}r^3\sin(\theta) \Big|_{1}^{3}\ d\theta\)

\(\displaystyle =\int_{0}^{2\pi} (\frac{1}{4}(3)^4\sin(\theta)\cos(\theta)+\frac{1}{3}(3)^3\sin(\theta))-(\frac{1}{4}(1)^4\sin(\theta)\cos(\theta)+\frac{1}{3}(1)^3\sin(\theta)) \ d\theta\)

\(\displaystyle =\int_{0}^{2\pi} (\frac{81}{4}\sin(\theta)\cos(\theta)+9\sin(\theta))-(\frac{1}{4}\sin(\theta)\cos(\theta)+\frac{1}{3}\sin(\theta)) \ d\theta\)

\(\displaystyle =\int_{0}^{2\pi} 20\sin(\theta)\cos(\theta)+\frac{26}{3}\sin(\theta) \ d\theta\)

\(\displaystyle = -\frac{1}{2}\cdot20\cos^2(\theta)-\frac{26}{3}\cos(\theta)\Big|_{0}^{2\pi}\)

\(\displaystyle = -\frac{1}{2}\cdot20\cos^2(2\pi)-\frac{26}{3}\cos(2\pi)-(-\frac{1}{2}\cdot20\cos^2(0)-\frac{26}{3}\cos(0))\)

\(\displaystyle = -\frac{1}{2}\cdot20(1)-\frac{26}{3}(1)-(-\frac{1}{2}\cdot20(1)-\frac{26}{3}(1))\)

\(\displaystyle = -10-\frac{26}{3}-(-10-\frac{26}{3})=0\)

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