Sửa đề:
`(x + 2)(x + 4)^2(x + 8) - 63x^2`
Giải:
`(x + 2)(x + 4)^2(x + 8) - 63x^2`
`= [(x + 2)(x + 8)][(x + 4)(x + 4)] - 63x^2`
`= (x^2 + 8x + 2x + 16)(x^2 + 4x + 4x + 16) - 63x^2`
`= (x^2 + 10x + 16)(x^2 + 8x + 16) - 63x^2`
`= (x^2 + 9x + 16 + x)(x^2 + 9x + 16 - x) - 63x^2`
`= (x^2 + 9x + 16)^2 - x^2 - 63x^2`
`= (x^2 + 9x + 16)^2 - 64x^2`
`= (x^2 + 9x + 16)^2 - (8x)^2`
`= (x^2 + 9x + 16 + 8x)(x^2 + 9x + 16 - 8x)`
`= (x^2 + 17x + 16)(x^2 + x + 16)`
