Question

当c=多少时,方程组｛ 2x-y=c+1 x+2y=2c 的解x和y相等

Answer 1

2x-y=c+1

y=2x-c-1

x+2y=2c

x+2(2x-c-1)=2c

x+4x-2c-2=2c

5x=2c+2c+2

x=(4c+2)/5=0.8c+0.4

y=2(0.8c+0.4)-c-1=1.6c+0.8-c-1=0.6c-0.2

x=y

0.6c-0.2=0.8c+0.4

0.8c-0.6c=-0.2-0.4

0.2c=-0.6

c=-3