已知x+y=-5,xy=7,求x2y+xy2-x-y的值.
问题描述:
已知x+y=-5,xy=7,求x2y+xy2-x-y的值.
答
x2y+xy2-x-y
=xy(x+y)-(x+y)
=(x+y)(xy-1)
∵x+y=-5,xy=7,
∴原式=-5×(7-1)=-30.