double integration part 3 evaluate by changing to polar coordinates

1.Evaluate Integration (from 0 to a) (Integration (from 0 to square root of (a^2 -x^2) square root (x^2+y^2)dydx
2.Evaluate double integral of e^-(x^2+y^2)dydx over the limits x=(0 to infinity) and y=(0 to infinity) by changing into polar coordinates