Câu 1 :
`A=2(x^{3}-y^{3})-3(x+y)^{2`
`=2(x-y)(x^{2}+y^{2}+xy)-3[(x-y)^{2}+4xy]`
Thay `x-y=2`
`->A=2.2.(2^{2}+3xy)-3(2^{2}+4xy)`
`=8+12xy-12-12xy`
`=-4`
Câu 2 :
`(x-y-1)^{3}-(x-y+1)^{3}+6(x-y)^{2}`
`=[(x-y)-1]^{3}-[(x-y)+1]^{3}+6(x-y)^{2}`
`=(x-y)^{2}-3(x-y)^{2}+3(x-y)-1-(x-y)^{3}-3(x-y)^{2}`
`=-3(x-y)-1+6(x-4)^{2}`
`=-2`