Ta có :\(\left(a+2\right)\left(x+3\right)\left(x+7\right)\left(x+8\right)-144\)
\(=\left(a+2\right)\left(x+7\right)\left(x+3\right)\left(x+8\right)-144\)
\(=\left(x^2-5x-14\right)\left(x^2-5x-24\right)-144\)
\(=\left(x^2-5x-14\right)\left(x^2-5x-24\right)-144\)
Đặt \(x^2-5x-14=t\) ta có:
\(t\left(t-10\right)-144\)
\(=t^2-10t-144\)
\(=\left(t-18\right)\left(t+8\right)\)
hay \(\left(x^2-5x-32\right)\left(x^2-5x-6\right)\)
\(=\left(x^2-5x-32\right)\left(x+1\right)\left(x-6\right)\)
b)