I've met a double integral which seems to be calcultated in polar system.
$\iint_D \frac {y} {x^2+y^2} dxdy$ , where $D$ is the region bounded by the following conditions:
$-2y \le x^2+y^2 \le -4y$;
$\frac {x} {\sqrt3} \le y \le 0$
I am not sure how to use the circle $x^2+y^2$ to calculate the double integral.