x+y=-5,xy=3,则-x^3y-xy^3+2x^2y^2等于

问题描述:

x+y=-5,xy=3,则-x^3y-xy^3+2x^2y^2等于

原式可化简为
xy(-x^2-y^2+2xy)
=xy(-x^2-y^2-2xy+4xy)
=xy(-(x+y)^2+4xy)
注:-x^2-y^2-2xy=-(x+y)
将1,2式代入得,
3*(-(-5)^2+4*3)
=-39