Chapter 8 - Section 8.1 - The Square Root Property and Completing the Square - Concept and Vocabulary Check - Page 592: 4

$x = 3i$ or $x=-3i$

$x^2 = -9$ Using the Square Root Property $u^2 = d$, then $u = \sqrt d$ or $u = - \sqrt d$. Thus, $x = \sqrt{-9}$ or $x = -\sqrt {-9}$ $x = \sqrt{9} \sqrt{-1}$ or $x = -\sqrt {9} \sqrt{-1}$ $x = 3i$ or $x=-3i$