\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 `3:`

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

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

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

`2, 1/2x^4y -3/2x^3y^4 +5/3x^4y -x^3y^4`

`=(1/2x^4y +5/3x^4y)+(-3/2x^3y^4 -x^3y^4)`

`=13/6x^4y -5/2x^3y^4`

`3, 5x-7xy^2 +3x-1/2xy^2`

`=(5x+3x)+(-7xy^2-1/2xy^2)`

`=8x-15/2xy^2`

`4, -1/5x^4y^3 +3/4x^2y -1/2x^2y +x^4y^3`

`=(-1/5x^4y^3 +x^4y^3)+(3/4x^2y -1/2x^2y)`

`=4/5x^4y^3 +1/4x^2y`