\(\Leftrightarrow x^2+2x-12x-24=0\)
\(\Leftrightarrow x\left(x+2\right)-12\left(x+2\right)=0\)
\(\Leftrightarrow\left(x-12\right)\left(x+2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-12=0\\x+2=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=12\\x=-2\end{matrix}\right.\)