What are the critical points of $f(x) = x^{3} - 3 x^{2} - 9 x + 5$?

Explanation

1. 01

   Critical points are where $f'(x) = 0$: $f'(x) = 3 \left(x - 3\right) \left(x + 1\right)$.

2. 02

   So $x = -1, 3$.