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 there should not be any negative number in the square root, the domain of the function is $\"\"$ .

Differentiate $\"\"$ on each side with respect to $\"\"$ .

$\"\"$

Equate $\"\"$ to zero :

$\"\"$

$\"\"$ is undefined at $\"\"$ .

Since $\"\"$ is not in the domain, the critical point is $\"\"$ .

The critical point is $\"\"$ .