Chain Rule - Supporting Problem 2

Problem: 

Prove that if

  • $g(x)$ is differentiable at $a$
  • $f(x)$ is differentiable at $g(a)$
  • for all $\bar{\delta}\gt0$ there exists an $x$ in the interval $(a-\bar{\delta},a)\cup(a,a+\delta)$ such that $g(x)=g(a)$

are true then
\[
\lim_{x\to a}\frac{f(g(x))-f(g(a))}{x-a}=0.
\]

Answer: