Verify the first special case of the chain rule for the composition focfoc in each of the cases.(a) f(x, y)=xy, c(t)=(et, cos(t))f(x, y)=xy, c(t)=(et, cos⁡(t)).(b) f(x, y)=x exp(x2+y2), c(t)=(t, −t)f(x, y)=x exp(x2+y2), c(t)=(t, −t).