\[x^{2} - 6x + 8 = x^{2} - 6x + 9 - 1 =\]
\[= (x - 3)^{2} - 1 =\]
\[= (x - 3 - 1)(x - 3 + 1) =\]
\[= (x - 4)(x - 2)\]