PTTNT 21`x^2``y^3`+28`x^4``y^2`-25`x^2``y^4`

Đáp án:

 `21x^{2}y^{3}+28x^{4}y^{2}-35x^{2}y^{4}`

`=x^{2}y^{2}.21y+x^{2}y^{2}.28x^{2}-x^{2}y^{2}.35y^{2}`

`=x^{2}y^{2}.(21y+28x^{2}-35y^{2})`

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