Answer
$-4\sqrt{5}$.
Work Step by Step
The given expression is
$=-\sqrt{80}$
Factor as square terms.
$=-\sqrt{16\cdot 5}$
Use product property of square roots.
$=-\sqrt{16}\cdot \sqrt{5}$
Use $16=4^2$.
$=-\sqrt{4^2}\cdot \sqrt{5}$
Simplify.
$=-4\sqrt{5}$.
