I have to evaluate the integral between 0 and 2a of the integral between 0 and sqrt(2ax-x^2) of x^2 dxdy

I am supposed to draw a diagram and draw a radial slice and I have to convert to polar co-ordinates.

The only thing I know how to do is x becomes rcos(theta) and dxdy becomes r dr dtheta

Any help would be great thanks.