Verify the first special case of the chain rule for the composition f c in each of the cases.
a) f(x, y) = xy,. c(t) - (e^t, cos(t))
b) f(x, y) = e^xy e(t) = (8t^2, t^3)
c) f(x, y) = (x^2 + y^2) log (square squareroot x^2 + y^2), e(t) = (e^t, e^-t)
d) f(x, y) = x exp(x^2 + y^2), e(t) = (t, -t)