$(x^{2}+x)^{2}+4(x^{2}+x)=12$ $<=> $(x^{2}+x)^{2}+4(x^{2}+x)+4=16$ <=> $(x^{2}+x+2)^{2}=16$
<=> $\left\{\begin{matrix} x^{2}+x+2=4 & & \\ x^{2}+x+2=-4 & & \end{matrix}\right.$
<=> $\left\{\begin{matrix} x^{2}+x-2=0 & & \\ x^{2}+x+6=0 & & \end{matrix}\right.$
<=> $\left\{\begin{matrix} (x-1)(x+2)=0 & & \\ (x+\frac{1}{2})^{2}+\frac{23}{4}>0 & & \end{matrix}\right.$
<=> $\begin{bmatrix} x=1 & & \\ x=-2 & & \end{bmatrix}$