# Help on easy integration

1. Feb 13, 2007

### JaysFan31

1. The problem statement, all variables and given/known data
I want to perform the following integration:
double integral of [(x^2)-(y^2)+2] dxdy where the function is subjected to the bound (x^2)+(y^2) greater than or equal to 2.

I'm trying to find the flux of a surface of a sphere (x^2)+(y^2)+(z^2)=9.

2. Relevant equations
Nothing, just rules of integration.

3. The attempt at a solution
Using Cartesian coordinates seems far too difficult. I could show you my work, but it's messy and complicated.
If I use parametrisation, then I get
double integral of [(r^2)cos^2(t)-(r^2)sin^2(t)+2) rdrdt
what are the bounds though?
t is between 0 and 2pi I'm pretty sure, but what about r?
It seems difficult since x^2+y^2 is greater than or equal to 2. This means that r^2 is greater than or equal to 2. Thus, it seems sqrt(2) is a lower bound, but what would the upper bound be?

Does this make any sense?

2. Feb 22, 2007

### gammamcc

For the trig part: Hint: http://www.sosmath.com/trig/Trig5/trig5/trig5.html
However, considering the bound you stated, it looks like your integral diverges.
If you integrate only where x>2 and y<1, you already get divergence.