Chapter 9 - Solving Quadratic Equations - 9.3 - Solving Quadratic Equations Using Square Roots - Exercises - Page 501: 19

$x=-3$

The given equation is $\Rightarrow (x+3)^2=0$ Take the square root of each side. $\Rightarrow x+3=\pm\sqrt {0}$ Simplify. $\Rightarrow x+3=0$ Subtract $3$ from each side. $\Rightarrow x+3-3=0-3$ Simplify. $\Rightarrow x=-3$ Hence, the solution is $x=-3$.