#### Answer

$-3i\sqrt2$

#### Work Step by Step

Factor the radicand so that one factor is a perfect square then simplify to obtain:
$=-\sqrt{9(-2)}
\\=-\sqrt{3^2(-2)}
\\=-3\sqrt{-2}$
Factor out $-1$ in the radicand to obtain:
$=-3\sqrt{-1(2)}$
Since $\sqrt{-1} = i$, bring out the square root of $-1$, which is $i$, to obtain:
$=-3i\sqrt2$