\[x² + 12x = 0\]
\[x(x + 12) = 0\]
\[x = 0,\ \ x + 12 = 0\]
\[\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x = - 12\]
\[Ответ:x = 0;\ x = - 12.\]