\[x^{2} + 12x + 11 =\]
\[= x^{2} + 12x + 36 - 25 =\]
\[= (x + 6)^{2} - 25 =\]
\[= (x + 6 - 5)(x + 6 + 5) =\]
\[= (x + 1)(x + 11)\]