\[x^{2} - 6x + 8 < 0\]
\[D_{1} = 9 - 8 = 1\]
\[x_{1} = 3 + 1 = 4;\]
\[x_{2} = 3 - 1 = 2;\]
\[(x - 2)(x - 4) < 0\]
\[2 < x < 4.\]