Question

Phân tích: a, ( a+1) (a+3)(a+5)(a+7)+15

Answer 1

\(a=\left(a+1\right)\left(a+3\right)\left(a+5\right)\left(a+7\right)+15\)

\(a=\left(a+1\right)\left(a+7\right)\left(a+3\right)\left(a+5\right)+15\)

\(a=\left(a^2+7a+a+7\right)\left(a^2+5a+3a+15\right)+15\)

\(a=\left(a^2+8a+7\right)\left(a^2+8a+15\right)+15\)

\(a=\left(a^2+8a+11-4\right)\left(a^2+8a+11+4\right)+15\)

\(a=\left(a^2+8a+11\right)^2-16+15\)

\(a=\left(a^2+8a+11\right)^2-1\)

\(a=\left(a^2+8a+11+1\right)\left(a^2+8a+11-1\right)\)

\(a=\left(a^2+8a+12\right)\left(a^2+8a+10\right)\)