已知x+y=5,xy=3,求代数式x^3y-2x^y^2+xy^3RT
问题描述:
已知x+y=5,xy=3,求代数式x^3y-2x^y^2+xy^3
RT
答
x^3y-2x^y^2+xy^3
=xy(x^2+2xy+y^2-4xy )
=xy[(x+y)^2-4xy]
=3*(5^2-4*3)
=3*13
=39