\begin{array}{c} \color{#FFFFFFff}{F}\color{#D0E4FFff}{u}\color{#A4C8FFff}{r}\color{#78ACFFff}{i}\color{#4C90FFff}{n}\color{#2064FFff}{a} \color{#0040A4ff}{F}\color{#2064FFff}{o}\color{#4C90FFff}{r}\color{#78ACFFff}{c}\color{#A4C8FFff}{a}\color{#D0E4FFff}{l}\color{#FFFFFFff}{o}\color{#D0E4FFff}{s} \end{array}

Bài `1:`

`1, A=3x^2y^4 +5x^3y^2 -7x^2y +xy -3x^2y^4`

`=(3x^2y^4-3x^2y^4)+5x^3y^2-7x^2y +xy`

`=5x^3y^2 -7x^2y +xy`

Bậc `:5`

`2, B=7x^2y(-4x^3y^5) +17x^2y^3 -4x^2y +28x^5y^6`

`=-28x^5y^6 +17x^2y^3 -4x^2y +28x^5y^6`

`=17x^2y^3 -4x^2y`

Bậc `:5`

`3, C=5x^4y^2 -7x^3y^2(-2xy^2)-5x^4y^2 +x^3-14x^4y^4`

`=5x^4y^2 +14x^4y^4 -5x^4y^2 +x^3 -14x^4y^4`

`=x^3`

Bậc `:3`

`4, D=-3x^2y(-2xy^2) +4xy -2 -6x^3y^3`

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

`=4xy -2`

Bậc `:2`