`(x+2)(x+3)(x+4)(x+5)-24`
`=[(x+2)(x+5)][(x+3)(x+4)]-24`
`=(x^2 +5x +2x+10)(x^2 +4x + 3x+12)-24`
`=(x^2 +7x+10)(x^2 +7x+12)-24`
`@` Đặt `x^2 +7x +11=t`
`=(t-1)(t+1)-24`
`=t^2 -1 -24`
`=t^2 -25`
`=(t-5)(t+5)`
`=(x^2 +7x +11 -5)(x^2 +7x +11+5)`
`=(x^2 +7x +6)(x^2 +7x +16)`