`t)x^3+6x^2+12x+8`
`=x^3+3.x^2 .2+2.x.2^2+2^3`
`=(x+3)^3`
`u)x^3-3x^2+3x-1`
`=x^3-3.x^2 .1+3.x.1^2-1^3`
`=(x-1)^3`
`v)1-9x+27x^2-27x^3`
`=1^3-3.1^2 .3x+3.1.(3x)^2-(3x)^3`
`=(1-3x)^3`
Áp dụng hằng đẳng thức:
`(a+b)^3=a^3+3a^2b+3ab^2+b^3`
`(a-b)^3=a^3-3ab^2+3ab^2+b^3.`