Verify Green's theorem for the disc D with center (0,0) and radius R and the following functions.
(a) P(x, y)=8 xy², Q(x, y)=-8yx²
(b) P(x, y)=x+y, Q(x, y)=9y
(c) P(x, y)=2 x y=Q(x, y)
(d) P(x, y)=2 y, Q(x, y)=x