已知x-y=-1,xy=3,求x³y-2x²y²+xy³的值

已知x-y=-1,xy=3,求x³y-2x²y²+xy³的值
已知x-y=-1,xy=3,求x³y-2x²y²+xy³的值

已知x-y=-1,xy=3,求x³y-2x²y²+xy³的值
x^3y-2x^2y^2+xy^3
因式分解先
=xy(x^2-2xy+y^2)
=xy(x-y)^2
好了,全部代入
=3

原式=XY(X²－2XY+Y²)=XY（X-Y）²=3（-1）²=3