bài2
câu 9
\(x^3-4x^2+x+6=\left(x^3+3x^2+3x+1\right)-7\left(x^2+2x+1\right)+12\left(x+1\right)=\left(x+1\right)\left[\left(x+1\right)^2-7\left(x+1\right)+12\right]\)\(=\left(x+1\right)\left(x^2-5x+6\right)=\left(x+1\right)\left(x-2\right)\left(x-3\right)\)