Answer
$8y^{10}$
Work Step by Step
$\sqrt (64y^{20})=8y^{10}$, because $(8y^{10})^{2}=8y^{10}\times 8y^{10}=(8\times8)\times(y^{10}\times y^{10})=64y^{20}$
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.