#### Answer

The domain is $(- \infty, 2]$

#### Work Step by Step

In order to compute the domain of the given function, we will first exclude those values of $x$ that will make the function undefined.
The square root function is undefined for negative numbers because the square root of a negative number is an imaginary number.
So, we can write
$2 -x \geq 0 \\ -x \geq -2 \\ x \leq 2$
This shows that the value of $x$ can be any real number less than or equal to $2$.
So, the domain is $(- \infty, 2]$