A function f : ℝ → ℝ is called even if f(x) = f(-x) for all x, and f : ℝ → ℝ is called odd if f(x) = -f(-x) for all x. Prove that if f : ℝ → ℝ is differentiable and odd, f' : ℝ → ℝ is even.

a) True
b) False