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_数学解答

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

人气：450 ℃　时间：2020-04-10 02:26:09

解答

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