`x(x + 4)(x + 6)(x + 10) + 128`
`=[x(x + 10)][(x + 4)(x + 6)] + 128`
`=(x^2+10x)(x^2+10x+24)+ 128`
Đặt `x^2+10x+12=y`
`⇒(x^2+10x)(x^2+10x+24)+ 128`
`=(y-12)(y+12)+ 128`
`=y^2-144+ 128`
`=y^2-144+ 128`
`=y^2-16`
`=(y-4)(y+4)`
Thay `x^2+10x+12=y`, ta được:
`(x^2+10x+12-4)(x^2+10x+12+4)`
`=(x^2+10x+8)(x^2+10x+16).`