## Calculus (3rd Edition)

$f'(x)$ exists for all x. Therefore, the only critical points are the solutions of $f′(x)=0$ $f'(x)=3x^{2}-9x-54=0$ Or $x^{2}-3x-18=0$ $\implies x= 6$ or $x=-3$ Thus, the critical points are the roots $c=6$ and $c=-3$.