Final answer:
To find the x-values for which f is not differentiable, we need to look for any points where the derivative of f does not exist. These points are called discontinuities.
Step-by-step explanation:
To find the x-values for which f is not differentiable, we need to look for any points where the derivative of f does not exist. The derivative of a function f(x) is undefined at any point where there is a sharp corner or a vertical tangent line on the graph. These points are called discontinuities. So, to find the x-values for which f is not differentiable, we need to identify any points on the graph of f where there are sharp corners or vertical tangent lines.