Đáp án `+` giải thích các bước giải:

`a, (x-2y)^3 - x^3 + 8y^3`

`= x^3 - 6x^2 y + 12xy^2 - 8y^3 - x^3 + 8y^3`

`= -6x^2 y + 12xy^2 + 8y^3`

`b, (x+y/2)^3 - (x - y/2)^3`

`= x^3 + 3/2 x^2 y + 3/4 xy^2 + (y^3)/8 - x^3 + 3/2 x^2 y - 3/4 xy^2 + (y^3)/8`

`= 3x^2 y + (y^3)/4`

`c, (2x - y)^3 + (2x + y)^3`

`= 8x^3 - 12x^2 y + 6xy^2 - y^3 + 8x^3 + 12x^2 y + 6xy^2 + y^3`

`= 16x^3 + 12xy^2`

`d, (2x + 3)(4x^2 - 6x + 9) - (25 + 8x^3)`

`= 8x^3 + 27 - 26 - 8x^3`

`= 1`

`e, (x-1)(x^2 + x + 1) - (x+1)(x^2 - x +1)`

`= x^3 - 1 - x^3 - 1`

`= -2`