\[x^{2} - 6x + 8 \leq 0\]
\[D_{1} = 9 - 8 = 1\]
\[x_{1} = 3 + 1 = 4;\ \ x_{2} = 3 - 1 = 2.\]
\[(x - 2)(x - 4) \leq 0\]
\[2 \leq x \leq 4.\]
\[\left\{ \begin{matrix} 2 \leq x \leq 4 \\ x < 3\ \ \ \ \ \ \ \ \ \\ \end{matrix} \right.\ \rightarrow 2 \leq x < 3.\]
\[Ответ:2 \leq x < 3.\]