Answer
$x=-6,2$
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 $x$.
$x^2+4x=12$
$(\frac{4}{2})^2=(2)^2$
$x^2+4x+(2)^2=12+(2)^2$
$x^2+4x+4=12+4$
$x^2+4x+4=16$
$(x+2)^2=16$
$x+2=±4$
$x=-2±4$
$x=-6,2$
