Chapter 10 - Section 10.6 - Radical Equations and Problem Solving - Exercise Set - Page 728: 26

$x=45$

$-\sqrt {3x+9}=-12$ $-1*-\sqrt {3x+9}=-12*-1$ $\sqrt {3x+9}=12$ $(\sqrt {3x+9})^2=12^2$ $3x+9=144$ $3x+9-9=144-9$ $3x=135$ $3x/3=135/3$ $x=45$ $-\sqrt {3x+9}=-12$ $-\sqrt {3*45+9}=-12$ $-\sqrt {135+9}=-12$ $-\sqrt {144}=-12$ $-12=-12$ (true)