Answer
$-\frac{\sqrt{7}}{9}$.
Work Step by Step
The given expression is
$=-\sqrt{\frac{7}{81}}$
Use quotient property of square roots.
$=-\frac{\sqrt{7}}{\sqrt{81}}$
Use $81=9^2$.
$=-\frac{\sqrt{7}}{\sqrt{9^2}}$
Simplify.
$=-\frac{\sqrt{7}}{9}$.
