已知x+xy=20,xy+x= -10,求下列代数式的值
问题描述：
已知x+xy=20,xy+x= -10,求下列代数式的值
1.3-4x-4xy+1/2xy+1/2y 2.x-y
3.x+2xy+y
答
3-4x-4xy+1/2xy+1/2y
=3-80+1/2xy+1/2y
=3-80-5
=-82
x-y
=(x+xy)-(xy+y)
=20+10
=30
x+2xy+y
=(x+xy)+(xy+y)
=20-10
=10