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