\[x^{2} + 8x + 7 =\]
\[= x^{2} + 8x + 16 - 9 =\]
\[= (x + 4)^{2} - 9 =\]
\[= (x + 4 - 3)(x + 4 + 3) =\]
\[= (x + 1)(x + 7)\]