Answer
$2\sqrt 10$
Work Step by Step
$\sqrt 40=\sqrt (4\times10)=\sqrt 4\times\sqrt 10=2\sqrt 10$
We know that $\sqrt 4=2$, because $2^{2}=4$.
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.