Chapter 1 - Equations and Inequalities - 1.7 Inequalities - 1.7 Exercises - Page 159: 47

$[-3,3]$

Step 1. Rewrite the inequality as $x^2-9\le0$ Step 2. Factor the quadratic, we have $(x+3)(x-3)\le0$ Step 3. The boundary points are $x=-3$ and $x=3$ Step 4. Use test points at $x=-4, 0, 4$, the signs of the quadratic are $+, -, +$ Step 5. The inequality requires negative, thus the solution interval (middle region) is $[-3,3]$