若x-y=3,xy=7,则xy^2-x^2y=?,x^2+y^2=?
问题描述:
若x-y=3,xy=7,则xy^2-x^2y=?,x^2+y^2=?
答
xy^2-x^2y=xy(x-y)=3×7=21
x^2+y^2=(x-y)^2+2xy=3^2+2×7=9+14=23