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Đáp án+Giải thích các bước giải:

 `a)`

`A=-4x^{2}y^{3}.(2x-3y)-2xy.(-4x^{2}y^{2}-4xy^{3})`

`=-8x^{3}y^{3}+12x^{2}y^{4}+8x^{3}y^{3}+8x^{2}y^{4}`

`=(8x^{3}y^{3}-8x^{3}y^{3})+(12x^{2}y^{4}+8x^{2}y^{4})`

`=20x^{2}y^{4}`

Vậy `A=20x^{2}y^{4}`

`b)`

`B=xy.(x^{2}-3x+4)-x^{2}y.(x+3)+6xy`

`=x^{3}y-3x^{2}y+4xy-x^{3}y-3x^{2}y+6xy`

`=(x^{3}y-x^{3}y)-(3x^{2}y+3x^{2}y)+6xy+4xy`

`=-6x^{2}y+10xy`

Vậy `B=-6x^{2}y+10xy`

`c)`

`C=(x^{2}+xy+y^{2}).(-2xy)+xy.(x^{2}-xy+y^{2})`

`=-2x^{3}y-2x^{2}y^{2}-2xy^{3}+x^{3}y-x^{2}y^{2}+xy^{3}`

`=(-2x^{3}y+x^{3}y)-(2x^{2}y^{2}+x^{2}y^{2})-(2xy^{3}-xy^{3})`

`=-x^{3}y-3x^{2}y^{2}-xy^{3}`

Vậy `C=-x^{3}y-3x^{2}y^{2}-xy^{3}`

`d)`

`D=3x.(4/3x-1)-4x.(-1/2x+3)+15x`

`=4x^{2}-3x+2x^{2}-12x+15x`

`=(4x^{2}+2x^{2})+(15x-12x-3x)`

`=6x^{2}`

Vậy `D=6x^{2}`