Let f (x) be differentiable at x = 0, and f (0) = 0, then find the following limit, where a is not equal to 0 and is a constant lim x→0 [ f(ax)-f(-ax)]/x

Let f (x) be differentiable at x = 0, and f (0) = 0, then find the following limit, where a is not equal to 0 and is a constant lim x→0 [ f(ax)-f(-ax)]/x

The answer is 2 * a * f '(0) (f' (0) is derivative)