Đáp án + Giải thích các bước giải:
`a)`
`(3x+1)^3=(3x)^3+3.(3x)^2 .1+3.3x.1^2+1^3`
`=27x^3+27x^2+9x+1`
`b)`
`(x/3-1)^3=(x/3)^3-3 . (x/3)^2 . 1 + 3 . x/3 . 1 - 1^3`
`=(x^3)/27 - (x^2)/3 + x - 1`
`c)`
`(-y^2+3x)^3=(-y^2)^3+3.(-y^2)^2 . 3x+3.(-y)^2.(3x)^2+(3x)^3`
`=-y^6+9xy^4-27x^2y^2+27x^3`
`d)`
`(x/y-(2y)/x)^3=(x/y)^3-3 . (x/y)^2 . (2y)/x+3 . x/y . ((2y)/x)^2 - ((2y)/x)^3`
`=(x^3)/(y^3)-6x+12y-(8y^3)/(y^3)`