\[4x² + 12x + 9 = 0\]
\[(2x + 3)^{2} = 0\]
\[2x + 3 = 0\]
\[2x = - 3\]
\[x = - \frac{3}{2} = - 1,5\]
\[Ответ:\ x = - 1,5.\]