Answer
$=(\sqrt{-9})^2==(\sqrt{9}\cdot \sqrt {-1})^2=(\sqrt{9})^2\cdot (i)^2=-9$.
Work Step by Step
The given expression is
$=(\sqrt{-9})^2$
Rewrite as shown below.
$=(\sqrt{9}\cdot \sqrt {-1})^2$
$=(\sqrt{9})^2\cdot (\sqrt {-1})^2$
Use $ \sqrt {-1}=i$
$=(\sqrt{9})^2\cdot (i)^2$
Use $i^2=-1$
Simplify.
$=-9$.
