Solving for Volume in a Complex Figure: Ostrogradsky and Spherical Coordinates

DianaSagita
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Volume Integral! Help!

I need help with this:

Find volume of figure bounded with surface (x^2+y^2+z^2+1)^2=8*(x^2+y^2)

I tried Ostrogradsky, and spherical coordinate system with it, but I can't find boundaries...

PLEASE! HELP ME!
 
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Welcome to PF!

DianaSagita said:
I need help with this:

Find volume of figure bounded with surface (x^2+y^2+z^2+1)^2=8*(x^2+y^2)

I tried Ostrogradsky, and spherical coordinate system with it, but I can't find boundaries...

PLEASE! HELP ME!

Hi DianaSagita ! Welcome to PF! :smile:

(what's Ostrogradsky? :confused: )

(oh, have a squared: ²)

Hint: it's obviously cylindrically symmetric, so write x² + y² = r², to give:

(r² + z² + 1)² - 8r² = 0. :smile:
 
Thanks a lot. I did it! :)
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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