Bài `5:`

`a, 2x^2y^2(x^3y^2 -x^2y^3-1/2y^5)`

`=2x^2y^2 . x^3y^2 - 2x^2y^2 . x^2y^3 -2x^2y^2 . 1/2y^5`

`=2x^5y^4 -2x^4y^5 -x^2y^7`

`b, -1/3xy(3x^3y^2-6x^2+y^2)`

`=-1/3xy . 3x^3y^2 -(-1/3xy) . 6x^2 + (-1/3xy) . y^2`

`=-x^4y^3 +2x^3y -1/3xy^3`

 `c, (-2xy^2 +2/3y^2 +4xy^2) . 3/2xy`

`=-2xy^2 . 3/2xy +2/3y^2 . 3/2xy +4xy^2 . 3/2xy`

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

`=3x^2y^3 +xy^3`

`d, (x^2+2xy-3)(-xy)`

`=x^2 . (-xy)+2xy . (-xy)-3 . (-xy)`

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

`e, 1/2x^2y(2x^3 -2/5xy^2-1)`

`=1/2x^2y . 2x^3 -1/2x^2y  . 2/5xy^2 -1/2x^2y . 1`

`=x^5y -1/5x^3y^3 -1/2x^2y`

`f, (-xy^2)^2 . (x^2-2x+1)`

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

`=x^4y^4 -2x^3y^4 +x^2y^4`