Answer
The domain is the set of real numbers less than or equal to $8$.
Work Step by Step
The given function is
$f(x)=\sqrt{-x+8}$
The radicand cannot be negative.
So, $-x+8$ is greater than or equal to zero.
$\Rightarrow -x+8\geq 0$
Add $x$ to each side.
$\Rightarrow 8\geq x$
Hence, the domain is the set of real numbers less than or equal to $8$.
