\[\left( \sqrt{x^{2} + 6x + 9} \right)^{2} = (2)^{2}\]
\[x^{2} + 6x + 9 = 4\]
\[x^{2} + 6x + 5 = 0\]
\[D = 36 - 20 = 16\]
\[x_{1,2} = \frac{- 6 \pm 4}{2} = - 1;\ - 5.\]
\[(x + 1)(x + 5) = 0\]
\[Ответ:\ - 1; - 5.\]