Answer
$9+2i$
Work Step by Step
Using the properties of radicals and that $i=\sqrt{-1}$, then the given expression, $
9+\sqrt{-4}
,$ is equivalent to
\begin{array}{l}\require{cancel}
9+\sqrt{-1}\cdot\sqrt{4}
\\\\=
9+i\cdot\sqrt{(2)^2}
\\\\=
9+i\cdot2
\\\\=
9+2i
.\end{array}
