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-y3.x+2xy+y
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
题目有问题····
答
x+xy=20,xy+x= -10,
不对
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
答
已知条件有错? 大概是①x+xy=20
，②xy+y=-10吧!
1.3-4(x+xy)+1/2(xy+y)
=3-4x20+1/2(-10)
=-82
2.x-y
=①-②
=30
3.x+2xy+y
=(x+xy)+(xy+y)
=20-10
=10