\[\sqrt{x^{2} - 6x + 12} = 2\]
\[t = x^{2} - 6x + 12\]
\[\sqrt{t} = 2\]
\[t = 4 \Longrightarrow x^{2} - 16x + 12 = 4\]
\[x^{2} - 6x + 12 - 4 = 0\]
\[x^{2} - 6x + 8 = 0\]
\[x_{1} = 4;\ \ \ \ x_{2} = 2\]
\[Ответ:4;2.\ \]