Critical number :

A critical number of a function $\"\"$ is a number $\"\"$ in the domain of $\"\"$ such that either $\"\"$ or $\"\"$ \ \ does not exist.

$\"\"$

The function is $\"\"$ .

Since $\"\"$ is a absolute function, it is not differentiable at $\"\"$ .

Equate $\"\"$ to zero.

$\"\"$

The critical point is $\"\"$ .