# Help with an integral

1. Nov 27, 2008

### eoghan

Hi there!
I have to calculate the integral of the function sqrt(x^2+y^2) over the circle (x-1)^2+y^2<=1

I use polar coordinates: rho goes from 0 to 2cos(theta) and theta goes from 0 to 2pi.
My result is that the integral is 0... is it right?

2. Nov 27, 2008

### jeffreydk

Yea I did it and got 0 because you end up integrating $\cos(\theta)^3$ at the end, which is 0.

3. Nov 27, 2008

eohgan, if you think about what the geometric meaning of the integral is, it should be clear as to why your answer is zero.

4. Nov 27, 2008

### tiny-tim

Hi eoghan!

erm … doesn't theta go from -π/2 to π/2?