用加减法解下列方程组 3(x+y)-4(x-y)=1 (x+y)/2+(x-y)/6=1

3(x+y)-4(x-y)=1 (1)
(x+y)/2+(x-y)/6=1
3(x+y)+(x-y)=6 (2)
由(2)-(1)得
5(x-y)=5
x-y=1 (3)
由(2)*4+(1)得
15(x+y)=25
x+y=5/3 (4)
由(3)+(4)得
2x=8/3
x=4/3
y=1/3