Converting Cartesian to Polar Coordinates for a Double Integral

[CaptainEvil]

I'm working on a double integral and need to change from cartesian to polar coords.

The double integral in cartesian coords is
Double integral from 0 to a (in dy) and from -sqrt(a^2 - y^2) in dx (NOTE minus sign before sqrt)

the little minus sign is troubling. How would I convert this region into polar coords?

 

[NoMoreExams]

I'm guessing your a is your radius? So what does y = ?

 

[CaptainEvil]

the whole question is

Double integral
(0 to a) (-sqrt(a^2 - y^2) to 0) of x^2y dxdy

 

[NoMoreExams]

Right, I'm asking you in polar coordinates, what does y =?

 

[CaptainEvil]

y = rsintheta

but I solved it, thanks anyway

 

[NoMoreExams]

Doesn't it equal a sin(theta) here?