Question

已知x-y=1,xy=2,则代数式x的3次方y-2x的2次方y的2次方+xy的3次方的值为

Answer 1

x^3y-2x^2y^2+xy^3

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

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

=(x-y)(x^2y-xy^2)

=(x-y)xy(x-y)

=2