Let f : be a convex function and let x1, x2, and x3 be three points in its domain such that x1

Let f : ℜ → ℜ be a convex function and let x1, x2, and x3 be three points in its domain such that x1 ≤ x2 ≤ x3. Show that f(x2) ≤ max{ f(x1), f(x3)}.