Differentiability

The checkboxes below will show you five different functions. Each function has at least one point at which it is not differential. Examine the functions one by one and determine the points at which they are not differential. There is a hint if you need it. Then discuss the questions below.
1) What are the different characteristics of a graph that will show you that it is not differentiable at that point? 2) What is it about each one that causes it to not be differentiable? (Be specific.)