Answer
$ f''(g(x))(g'(x))^{2}+f'(g(x))g''(x)$
Work Step by Step
Applying the chain rule, we have
$(f\circ g)'=f'(g(x))\times g'(x)$
$(f\circ g)''= \frac{d}{dx}[f'(g(x))\times g'(x)]$
Applying the chain rule and the product rule, we get
$(f\circ g)''=f''(g(x))g'(x)\times g'(x)+f'(g(x))\times g''(x)$
$= f''(g(x))(g'(x))^{2}+f'(g(x))g''(x)$
