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