Question

Let f(x) = |x-9|. Evaluate the following limits.

\lim_{x\to 9^-} \frac{f(x)-f(9)}{x-9}=

\lim_{x\to 9^+} \frac{f(x)-f(9)}{x-9}=

Thus the function f(x) is not differentiable at 9.