giải hộ mình câu 1,2,3,4,5,6

`K`

Bài `2:`

`1, (x+1)^3 - (x-4)(x+4) -x^3`

`=x^3 + 3x^2 + 3x +1 -x^2 +16 -x^3`

`=(x^3-x^3) + (3x^2-x^2) +3x+(1+16)`

`=2x^2+3x+17`

`2, (x+2)^3 - x(x+3)(x-3) -12x^2-8`

`=x^3+6x^2+12x +8 -x(x^2-9) -12x^2-8`

`=x^3+6x^2 + 12x + 8-x^3 +9x -12x^2-8`

`=(x^3-x^3) + (6x^2-12x^2) + (12x+9x) + (8-8)`

`=-6x^2 + 21x`

`3, (x-2)^3-x(x-2)(x+2)+6x(x-3)`

`=x^3-6x^2+12x-8 -x(x^2-4)+6x^2-18x`

`=x^3 - 6x^2 +12x - 8 -x^3 +4x + 6x^2 -18x`

`=(x^3-x^3) + (-6x^2+6x^2) + (12x +4x-18x) -8`

`=-2x-8`

`4, x(x-5)(x+5) -(x-5)^3 +100x`

`=x(x^2-25) -(x^3-15x^2 + 75x -125) +100x`

`=x^3 - 25x -x^3+15x^2 - 75x +125 +100x`

`=(x^3-x^3) + (-25x-75x+100x) + 15x^2+125`

`=15x^2+125`

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

`=x^3-9x^2y + 27xy^2 - 27y^3 - x^2 + 4y^2`

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

`=-(x+2y)^3 + x(2y-x)(2y+x)`

`=-(x^3+6x^2y + 12xy^2 + 8y^3) + x(4y^2 -x^2)`

`=-x^3 -6x^2y -12xy^2 -8y^3 +4xy^2 - x^3`

`=(-x^3 -x^3) -6x^2y + (-12xy^2+4xy^2) -8y^3`

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