Chapter 2 - Linear and Quadratic Functions - Section 2.7 Complex Zeros of a Quadratic Function* - 2.7 Assess Your Understanding - Page 177: 6

$9i$

Note that $\sqrt{-81}=\sqrt{-1(81)}$ Use the Product Rule $\sqrt{a b}=\sqrt{a} \times \sqrt{b}$ to obtain $\begin{aligned} \sqrt{-1 \times 81} &=\sqrt{-1} \times \sqrt{81} \\ &=i \times \sqrt{9^{2}} \\ &=i \times 9 \\ &=9 i \end{aligned}$