Let y = f(x), choose the correct statement:
1
f is differentiable in [a, b] if f'(x) exist for all x ϵ (a, b)
2
f is differentiable in (a, b) if it is differentiable at x = a and x = b
3
f is differentiable in [a, b] if f'(a + 0) and f'(a - 0) exist
4
f is differentiable in (a, b) if it is differentiable in x ϵ (a, b)