Let f(x) be a differentiable function, and let (a, f(a)) be a critical point of f(x). Then,
1. If f”(a) > 0, then (a, f(a)) is a local minimum of f(x).
2. If f”(a) < 0, then (a, f(a)) is a local maximum of f(x).
3. If f”(a) = 0, then the second derivative test tells us nothing!
