4. T/F (with justification) If f(x) is a differentiable function on (a, b) and f(x) has a local maximum or minimum value at x = c in (a, b) then f'(c) = 0. I 5. T/F (with justification) If f(x) is a differentiable function on (a, b) and f'(c) = 0 for a number c in (a, b) then f(x) has a local maximum or minimum value at x = c.