1: =x^3-6x^2+12x-8+x^3+6x^2+12x-8
=2x^3+24x
2: =x^3-3x^2+3x-1-x^3-3x^2-3x-1
=-6x^2-2
3: =1-3x+3x^2-x^3+x^3+9x^2+27x+27
=24x+12x^2+28
4: =x^3+6x^2y+12xy^2+8y^3-x^3+6x^2y-12xy^2+8y^3
=12x^2y+16y^3
5: =y^3-3y^2x+3yx^2-x^3-8x^3+12x^2y-6xy^2+y^3
=2y^3-9xy^2+15x^2y-9x^3
7: =8x^3-36x^2+54x-27-2x(4x^2+4x+1)
=8x^3-36x^2+54x-27-8x^3-8x^2-2x
=-44x^2+52x-27
8: =27x^3-27x^2+9x-1-27x^3-27x^2
=-54x^2+9x-1