#### Answer

$9i$

#### Work Step by Step

Step 1: $\sqrt -81$= $\sqrt -1\times\sqrt 81$
Step 2: Since $\sqrt -1=i$, the expression becomes $i\sqrt 81$
Step 3: Simplifying further, $i\sqrt 81$= $i\times9$ = $9i$

Published by
Pearson

ISBN 10:
0321726391

ISBN 13:
978-0-32172-639-1

$9i$

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