Question

已知2(x+y)=-6,xy=1,求代数式(x+2)-(3xy-y)的ŀ

Answer 1

由2(x+y)=-6得x+y=-3,
(x+2)-(3xy-y)
=x+2-3xy+y
=x+y+2-3xy
=-3+2-3
=-4.

Answer 2

2(x+y)=-6,xy=1,求代数式(x+2)-(3xy-y)的值
(x+2)-(3xy-y)=x+2-3xy+y=x+y+2-3xy 2(x+y)=-6 把 x+y=-3 xy=1代入x+y+2-3xy=-4