(a) Use the Product Rule twice to prove that if , , and are differentiable, then (fgh)' = fgh + fg'h + gfh'.
(b) Taking f = g = h in part (a), show that
d/dx[f(x)]3 = 3[f(x)]2 f'(x)
(c) Use part (b) to differentiate y = e3x.