Suppose f: R R is twice differentiable, i.e., f' is a differentiable function. Suppose that a, h ER and h> 0. Show that there exists c (a-h, a + h) such that Hint: Let g(x) g'(b) - f" (c) = g(b+h)-g(b) h f(a+h) 2(a) + f(a h) h f(x)-f(x-h) h " and show that there is a b (a, a + h) with