A=(x-y-1)³-(x-y+1)³+6(x-y)²

Giải thích các bước giải:

`A=(x-y-1)^3-(x-y+1)^3+6(x-y)^2`

`=(x-y-1-x+y-1)[(x-y-1)^2+(x-y-1)(x-y+1)+(x-y+1)^2]+6(x-y)^2`

`=-2[(x-y-1)^2+(x-y)^2-1+(x-y+1)^2]+6(x-y)^2`

`=-2(x-y-1)^2-2(x-y)^2+2-2(x-y+1)^2+6(x-y)^2`

`=-2(x-y-1)^2+4(x-y)^2+2-2(x-y+1)^2`

`=-2(x^2+y^2+1-2xy-2x+2y)+4(x^2-2xy+y^2)+2-2(x^2+y^2+1-2xy+2x-2y)`

`=-2x^2-2y^2-2+4xy+4x-4y+4x^2-8xy+4y^2-2x^2-2y^2-2+4xy-4x+4y+2`

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

`=-2`