Let (x) = x 3 3x + 1. Show that '(x) 3 for all x

Let ƒ(x) = x³ − 3x + 1. Show that ƒ'(x) ≥ −3 for all x and that, for every m > −3, there are precisely two points where ƒ'(x) = m. Indicate the position of these points and the corresponding tangent lines for one value of m in a sketch of the graph of ƒ.