(2) Suppose f: RR 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 f(a+h)-2f(a) + f(a - h) Hint: Let g(x) g' (b) f" (c) ƒ (x) − ƒ (x − h) h g(b+h) – g(b) h h² and show that there is a b E (a, a + h) with