Answer
$-6\sqrt{2}$.
Work Step by Step
The given expression is
$=-\sqrt{72}$
Factor as square terms.
$=-\sqrt{36\cdot 2}$
Use product property of square roots.
$=-\sqrt{36}\cdot \sqrt{2}$
Use $36=6^2$.
$=-\sqrt{6^2}\cdot \sqrt{2}$
Simplify.
$=-6\sqrt{2}$.
