Answer
$15i$
Work Step by Step
$\sqrt -225=\sqrt (-1\times225)=\sqrt -1\times\sqrt 225=i\times15=15i$
We know that $\sqrt -1=i$, because $i^{2}=-1$.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.