~ Bạn tham khảo ~
`4, (x-3)(x^2+3x+9)-(x^2-1)(x+27)`
`= (x-3)(x^2+3x+3^2)-x^2(x+27)+(x+27)`
`= x^3-3^3-x^3-27x^2+x+27`
`= -27x^2+x`
`5,(3-x)^3-(x+3)(x^2-3x+9)`
`= 27-27x+9x^2-x^3-x^3-3^3`
`= -27x+9x^2-2x^3`
`6,(x-2)(x^2+2x+4)-x(x-3)(x+3)`
`= x^3-2^3-x(x^2-3^2)`
`= x^3-8-x^3+9x`
`= 9x-8`
