I think this is similar to the answer provided for problem 3.5, but I am having a difficult time understanding why, in Problem 3.4, the error is continuous and differentiable at the point

. I have the three cases looking like this so far:

in which I believe

in which I believe

in which I believe

These cases would make

non-differentiable because the derivatives from the left and right are different. Am I evaluating the error from the book wrong -->

?