Solution
= Solution
Here $Q_x-P_y=y-2y=-y$. Green's theorem gives the <integral> of $-y$ over a region symmetric about the $x$ axis, hence the answer is $0$.
= Solution
Here $Q_x-P_y=y-2y=-y$. Green's theorem gives the <integral> of $-y$ over a region symmetric about the $x$ axis, hence the answer is $0$.