\(A=\left(a+1\right)\left(a+3\right)\left(a+5\right)\left(a+7\right)+15\)
\(=\left(a+2\right)\left(a+6\right)\left(a^2+8a+10\right)\)
\(A=\left(a+1\right).\left(a+3\right).\left(a+17\right)+15\)
\(=\left(a^2+8a+7\right)\left(a^2+8a+15\right)+15\)
\(=\left(a^2+8a+11-4\right)\left(a^2+8a+11+4\right)+15\)
\(=\left(a^2+8a+11\right)^2-4^2+15\)
\(=\left(a^2+8a+11\right)^2-1\)
\(=\left(a^2+8a+11-1\right)\left(a^2+8a+11+1\right)\)
\(=\left(a^2+8a+10\right)\left(a^2+8a+12\right)\)
(a2+8a+12) = (a2+2a+6a+12)
= (a+2) (a+6)
c) 2x2(x +1) + 4x(x +1); d) 2 x(y - 1) - 2
