Answer
The domain is $\{x\in\mathbb{R}|x\leq-2\}$.
Work Step by Step
For a square root to be defined, the function inside the root must be greater than or equal to $0$.
The domain is defined by applying the requirement:
$-x-2\geq0$
$-x-2+x\ge0+x$
$-2\geq x$
$x\le-2$
Therefore ,the domain is $\{x\in\mathbb{R}|x\leq-2\}$.
