Answer
$-4i\sqrt 5$
Work Step by Step
$-\sqrt -80=-(\sqrt (16\times5\times-1))=-(\sqrt 16\times\sqrt 5\times\sqrt -1)=-(4i\sqrt 5)=-4i\sqrt 5$
We know that $\sqrt 16=4$, because $4^{2}=16$.
We know that $\sqrt -1=i$, because $i^{2}=-1$.
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