For some constants a and b, let \(f(x) = \left\{ \begin{array}{cl} ax + b & \text{if } x < 2, \\ 8 - 3x & \text{if } x \ge 2. \end{array} \right.\) . The function f has the property that f(f(x)) = x for all x. What is a + b?
So I don't even know where to start with this one... can someone please explain how to do this?