Answer
$\{-7,3\}$
Work Step by Step
Complete the square by adding $\left(\frac{4}{2}\right)^2=4$ to both sides.
$x^2+4x+4=21+4$
Simplify.
$x^2+4x+4=25$
Factor on the left side.
$(x+2)^2=25$
Take the square root of both sdides:
$\sqrt{(x+2)^2}=\pm \sqrt {25}$
$x+2=\pm \sqrt {5^2}$
$x+2=\pm 5$
Split the expression to obtain:
$x+2=5\quad$ or $\quad x+2=-5$
Subtract $2$ from both sides of both equations.
$x+2-2=5-2\quad$ or $\quad x+2-2=-5-2$
Simplify.
$x=3\quad $ or $\quad x=-7$
Hence, the solution set is $\{-7,3\}$.
