Đáp án:
`1/2 x^2 (6x - 3) - x (x^2 + 1/2) (x + 4)`
`= 3x^3 - 3/2x^2 - (x^3 + 1/2x) (x + 4)`
`= 3x^3 - 3/2x^2 -[ x^3 (x + 4) + 1/2x (x + 4)]`
`= 3x^3 - 3/2x^2 - [x^4 + 4x^3 + 1/2x^2 + 2x]`
`= 3x^3 - 3/2x^2 - x^4 - 4x^3 - 1/2x^2 - 2x`
`= (3x^3 - 4x^3) + (-3/2x^2 - 1/2x^2) - x^4 - 2x`
`= -x^3 - 2x^2 - x^4 - 2x`