Answer
$x=-4,-2$
Work Step by Step
To complete the square, add a term that is the square of half the coefficient of $x$ to both sides of the equation, and factor the left side. Then use the square root property to simplify both sides, and then isolate $x$.
$x^2+6x=-8$
$(\frac{6}{2})^2=(3)^2$
$x^2+6x+(3)^2=-8+(3)^2$
$x^2+6x+9=-8+9$
$x^2+6x+9=1$
$(x+3)^2=1$
$x+3=±1$
$x=-3±1$
$x=-4,-2$
