Ta có : \(A=\left(x^3+y^3\right)-2\left(x^2-y^2\right)+3\left(x+y\right)^2=\left(x+y\right)\left(x^2+xy+y^2\right)-2\left(x+y\right)\left(x-y\right)+3\left(x+y\right)^2=\left(x+y\right)[(x^2+xy+y^2)-2\left(x-y\right)+3\left(x+y\right)]=(x+y)\left(x^2+y^2+xy+x+5y\right)\)Như vậy A Chia hết cho (x+y)