1. The problem statement, all variables and given/known data Where is the function f(x) = |x| differentiable? 2. Relevant equations [f(x+h) - f(x)] / h 3. The attempt at a solution I know that the graph of f(x)=|x| shows a corner at the origin from which 2 lines project at opposite slopes, as in they are symmetric about the y-axis. I've seen the solution but I don't understand why f(x) is differentiable for every number except 0.