Đáp án + Giải thích các bước giải:
`9.` `x^3-2x^2+2x-4=x^2(x-2)+2(x-2)=(x-2)(x^2+2)`
`10.` `xy-4+2x-2y=xy+2x-4-2y`
`=x(y+2)-2y-4`
`=x(y+2)-2(y+2)=(y+2)(x-2)`
`11.` `xy+1-x-y=xy-x+1-y`
`=x(y-1)-y+1`
`=x(y-1)-(y-1)=(y-1)(x-1)`
`12.` `x^2-y^2+4x+4=(x^2+4x+4)-y^2`
`=(x+2)^2-y^2=(x+2-y)(x+2+y)`.