Answer
$i\sqrt 24$
Work Step by Step
$\sqrt -3\times\sqrt -8=\sqrt (-1\times3)\times\sqrt (-1\times8)=\sqrt -1\times\sqrt 3\times\sqrt -1\times\sqrt 8=i\times i\times\sqrt (3\times8)=i^{2}\times\sqrt 24=-1\times\sqrt 24=i\sqrt 24$
We know that $\sqrt -1=i$, because $i^{2}=-1$.
