已知x+y=7,xy=2,则x³y-2x²y²+xy³等于?

问题描述:

已知x+y=7,xy=2,则x³y-2x²y²+xy³等于?

x³y-2x²y²+xy³
=xy(x²-2xy+y²)
=xy(x-y)²
=2×7²
=98