I tried to do the exercise below and I found the one-sided limits as 0, both left and right. But in the book the answer is -1 and 1.
Make the graph of the function. Determine if the function is continuous at $c$. Compute the lateral limits $f_-'(x_1)$ and $f_+'(x_1)$. $f(x)=|x-3|$; $x_1=3$.