How do I solve these questions?

3 (a) Show that E(-1)n n n=1 (n + 1)(n + 2) converges conditionally. (b) For n a natural number, let b(n) be the largest integer m so that 2" 0 and f(0) = 0. Show that there is e > 0 so that f(x) is positive for x E (0, c) and f(x) is negative for x E (-6, 0). (b) Let f(x) be an everywhere defined real-valued function on the reals. Suppose that f(x) is O(1) as r -> 0. Let g(x) = x4f (x). Show that g(x) is differentiable at r = 0