\[x^{2} - 6x + 5 = x^{2} - 6x + 9 - 4 =\]
\[= (x - 3)^{2} - 2^{2} =\]
\[= (x - 3 - 2)(x - 3 + 2) =\]
\[= (x - 5)(x - 1)\]