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Volume integrals

asked 2014-07-31 11:01:05 -0600

Tiffany gravatar image

updated 2014-07-31 11:01:31 -0600

I was wondering if when we are setting up volume integrals, if we always integrate as 1? then $\delta \rho \delta \phi \delta \theta$ ? or do we use the function, and then if it ends up being 1, we go with that?

For example number 5 on the review sheet for the final exam. It says

"Let S denote the unit sphere. Evaluate $$\iiint_S (x^2 + y^2 + z^2) dV$$ "

So I was wondering if we set it up as...

$$ \int _0 ^{2\pi} \int _0 ^\pi \int _0^1 \rho^2* \rho^2 \sin \phi \delta \rho \delta \phi \delta \theta $$

or $$ \int _0 ^ {2\pi} \int _0 ^\pi \int _0^1 1 * \rho^2 \sin \phi \delta \rho \delta \phi \delta \theta $$

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answered 2014-07-31 11:16:48 -0600

Anonymous gravatar image

So the only time that you want to evaluate an integral representing the volume of $D$ is when it is specifically asked. For example question #$4e$ off of the in-class worksheet from July 24th. Otherwise, always use the function given and convert it to whatever coordinate system you are going to use. So for this problem it would be: $$\int_0^{2\pi}\int_0^{\pi}\int_0^1 (\rho^2)\rho^2 \sin(\phi) d\rho d\phi d\Theta$$

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Asked: 2014-07-31 11:01:05 -0600

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Last updated: Jul 31 '14