加減消元法

x/3-y/4=2x+y___(1)
2x+y=4____(2)
(1)×12:4x-3y=24x+12y
20x+15y=0
4x+3y=0___(3)
(2)×2:4x+2y=8___(4)
(3)-(4):y=-8
Put y=-8 into (2)
2x-8=4
2x=12
x=6
The solution is x=6 and y=-8.

x/3-y/4=2x+y=4
x/3-y/4=4
2x+y=4
1x2:2(x/3-y/4)=8
2x/3-2y/4=8
2x-2y=96
2+3:3y=100
y=33.3
把y=33.3代入2
2x+33.3=4
x=-14.65