If f (0) = 0, f ′ (0) = a, then limf (x) / X is in X → 0=

If f (0) = 0, f ′ (0) = a, then limf (x) / X is in X → 0=

Limf (x) / x = limf [(x) - f (0)] / (x-0) when x → 0,
According to the definition of derivative, the result is f '(0) = a