Solve $$\iint_{D} {e}^{-(x^2+y^2)}dxdy$$ when $ D=\left \{ \left ( x,y \right ):x^2+y^2\leq R^2, 0\leq y\leq x \right \}$.
I have problems with how i should decide the intervals of the integrals? And what they are? $$\iint_{E} {e}^{-(r^2)}r drd\theta$$