The function is $\"\"$

Differentiate with respect to x.

$\"\"$

To find the critical numbers $\"\"$ and $\"\"$ does not exist.

$\"\"$

The function $\"\"$ does not exist when $\"\"$ .

$\"\"$

The imaginary numbers are negligible, the critical numbers are x = 0, x = 3 and x = -3.

$\"\"$

The critical points are $\"\"$ .