初一方程俎

2x-y=m+1(1)
x+2y=2m (2)

(1)×2+(2)得:
5X=4M+2
X=(4M+2)/5

(2)×2-(1)得:
5Y=3M-1
Y=(3M-1)/5

依题意得:

(4M+2)/5-(3M-1)/5=0
4M+2-3M+1=0
M+3=0
M=-3

故选C

方程组2x-y=m+1,x+2y=2m 满足x-y=0 则m=（） 选择答案有:A3 B4 C-3 D-4 (希望给出计算过程）

2x-y=m+1...(1)
x+2y=2m...(2)
(1)两边同乘以2,得4x-2y=2m+2...(3)
(2)+(3),得5x=4m+2,得x=(4m+2)/5
(2)两边同乘以2,得2x+4y=4m...(4)
(4)-(1),得5y=3m-1,得y=(3m-1)/5
x-y=0
(4m+2)/5-(3m-1)/5=0
解得m=-3

选C

2x-y=m+1,..(1)
x+2y=2m ....[2]

[1]*2+[2]:

5x=4m+2

x=(4m+2)/5

y=2x-(m+1)=(8m+4)/5-(m+1)=(3m-1)/5

x-y=(m+3)/5=0

m=-3

C