Question

Phân tích đa thức thành nhân tử:`(x+1)(x+2)(x+3)(x+4) + 25` 

Answer 1

\(\left(x+1\right)\left(x+2\right)\left(x+3\right)\left(x+4\right)-24\) (sửa đề)

\(=\left[\left(x+1\right)\left(x+4\right)\right].\left[\left(x+2\right).\left(x+3\right)\right]-24\)

\(=\left(x^2+5x+4\right)\left(x^2+5x+6\right)-24\)

Đặt \(y=x^2+5x+4\), thay vào đa thức, ta được:

\(y\left(y+2\right)-24\)

\(=y^2+2y-24\)

\(=\left(y^2+2y+1\right)-25\)

\(=\left(y+1\right)^2-5^2\)

\(=\left(y+1-5\right)\left(y+1+5\right)\)

\(=\left(y-4\right)\left(y+6\right)\)

\(=\left(x^2+5x+4-4\right)\left(x^2+5x+4+6\right)\)

\(=\left(x^2+5x\right)\left(x^2+5x+10\right)\)

\(=x\left(x+5\right)\left(x^2+5x+10\right)\)