Chapter 1, Equations and Inequalities - 1.7 Solve Absolute Value Equations and Inequalities - 1.7 Exercises - Skill Practice - Page 55: 9

$$x=-9\quad \mathrm{or}\quad \:x=9$$

Since the value inside the absolute value can be positive or negative and get the same number, we must consider both options. Doing this, we find: $$\left|x\right|=9 \\ x=-9\quad \mathrm{or}\quad \:x=9$$