Đáp án:

 

Giải thích các bước giải:

`2xy^2(B-x^3y)=2x^3 y^2 - 2x^4 y^3`

`=>B-x^3 y=(2x^3y^2-2x^4y^3) : 2xy^2`

`=>B-x^3 y = x^2 - x^3 y`

`=>B=x^3 - x^3y+x^3y`

`=>B=x^3`

Vậy `B=x^3`

_____________

`-5x^5 y (-xy^4 +B)=10x^5 y^5 + 5x^6y^5`

`=>-xy^4 +B = (10x^5 y^5 + 5x^6 y^5) : (-5x^5y)`

`=>-xy^4 + B=-2 y^4 - xy^4`

`=>B=-2y^4 - xy^4 + xy^4`

`=>B=-2y^4`

Vậy `B=-2y^4`

______________

`(4x^4 y^4 - 5/4 x^5 y^5) : 3x^2 y^2 = B-5/(12)x^3y`

`=>4/3 x^2 y^2 - 5/(12) x^3 y^3 = B-5/(12)x^3y`

`=>B-5/(12)x^3 y = 4/3 x^2y^2-5/(12)x^3y^3`

`=>B=4/3 x^2y^2 - 5/(12)x^3y^3 + 5/(12)x^3y`

Vậy `B=4/3x^2 y^2 - 5/(12)x^3 y^3 + 5/(12)x^3y`