Answer
-.9
Work Step by Step
We know that $\sqrt .81=.9$, because $.9^{2}=.9\times.9=.81$.
Therefore, $-\sqrt .81=-(.9)=-.9$.
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.