x3 + 2x2y + xy2 - 9x
= x( x2 + 2xy + y2 - 9 )
= x[ ( x2 + 2xy + y2 ) - 9 ]
= x[ ( x + y )2 - 32 ]
= x( x + y - 3 )( x + y + 3 )
Bài làm
\(x^3+2x^2y+xy^2-9x=x\left(x^2+2xy+y^2-9\right)\)
\(=x\left[\left(x+y\right)^2-9\right]=x\left(x+y-3\right)\left(x+y+3\right)\)