Answer
$x=-1\pm\sqrt{13}$
Work Step by Step
Using the completing the square method, the solutions of the given quadratic equation, $
x^2+2x-12=0
,$ is
\begin{array}{l}\require{cancel}
x^2+2x=12
\\\\
x^2+2x+\left( \dfrac{2}{2}\right)^2=12+\left( \dfrac{2}{2}\right)^2
\\\\
x^2+2x+1=12+1
\\\\
(x+1)^2=13
\\\\
x+1=\pm\sqrt{13}
\\\\
x=-1\pm\sqrt{13}
.\end{array}