Hey i have an ap calculus question

which of the following statements is/are true?

1. if f '(c) = 0, then f has a local maximum or minimum at x = c.
2. if f is continuous on [a, b] and differentiable on (a, b) and f '(x) = 0 on (a, b), then f is constant on [a, b].
3. the mean value theorem can be applied to f(x) = 1/x2 on the interval [−1, 1].