Answer
$2i$
Work Step by Step
Factor the radicand so that one factor is a perfect square and another is $-1$ to obtain:
$\sqrt{-4}=\sqrt{4(-1)}$
Use the rule $\sqrt{a\cdot b}=\sqrt{a} \cdot \sqrt{b}$ tp obtain:
$=\sqrt{4}\cdot \sqrt{-1}$
Use $\sqrt{4}=2$ and $\sqrt{-1}=i$:
$=2\cdot i$
$=2i$
Hence, the solution in the standard form is $2i$.
