Multiple Integration: rho = rt 6, z = x^2 + y^2

whizvish

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Oct 21, 2007
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Find the volume bounded by the sphere rho = rt. 6
and the paraboloid z = x^2 +y^2

And Locate the Centroid.
4deb41286077aabd94b30802f0e6a68a-1.gif


That is how I set up the integral.
But then I need help Solving the integral and finding the Centroid.
Please Help!! :(
 
Re: Multiple Integration Help~

I believe the r limits should be 0 to sqrt(2). Seems right.

\(\displaystyle z=r^{2}, \;\ z=\sqrt{6-r^{2}}\)

Because \(\displaystyle \sqrt{6-r^{2}}=r^{2}\), solve for \(\displaystyle r=\pm\sqrt{2}\)

\(\displaystyle \int_{0}^{2\pi}\int_{0}^{\sqrt{2}}\int_{r^{2}}^{\sqrt{6-r^{2}}}rdzdrd{\theta}\)

These things are tedious. Once you have the correct set up, run it thorugh a calculator.

The biggest part of them is setting up the proper integral. Then, most just solve them with tech.

I know I do.

\(\displaystyle \int_{r^{2}}^{\sqrt{6-r^{2}}}{r}dz=r(\sqrt{6-r^{2}}-r^{2})\)

\(\displaystyle \int[r(\sqrt{6-r^{2}}-r^{2})]dr=\frac{-(6-r^{2})^{\frac{3}{2}}}{3}-\frac{r^{4}}{4}\)

Now, use the limits for r, then theta is easy.
 
When I evaluated the integral. I got approx. 2.46pi. Does that seem right? I'm always second guessing myself when it comes to evaluating integrals.

And then what do I do to set up the centroid aspect of the problem?
Thanks for help. =)
 
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