`\ttcolor{maroon}{# Phương Anh}`

Bài `1:`

`a)`

`P = x(x^2-y) -x^2(x+y) +xy(x-2)`

`P = x. x^2-x.y-x^2 . x - x^2 . y + xy.x-xy.2`

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

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

`P = -3xy`

`b)` Thay `x=2, y=-3` vào `P,` có:

`P = -3. 2.(-3)`

`P = 3.2.3`

`P = 18`

Vậy `P=18` khi `x=2, y=-3`

Bài `2:`

`a)`

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

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

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

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

`Q = 4xy + 2x^2y`

`b)` Thay `x=-1` vào `Q,` có:

`Q = 4.(-1).y + 2.(-1)^2.y`

`Q = -4y+2y`

`Q=-2y`

Vậy `Q=-2y` khi `x=-1`