Solve for

<-- With ,

My book says that I need to square the left side and turn the right side into a double integral of and then convert u into r cos theta, v into r sin theta, and go from there. But that is where I get lost. Obviously that makes u^2 + v^2 = r^2, but what the heck do I do with (a) du and dv, and (b) the limits of integration?