2分子X+Y-3分子X-Y=6 3(X+Y)=4(X-Y) 老做不对,

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2分子X+Y-3分子X-Y=6 3(X+Y)=4(X-Y) 老做不对,
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2分子X+Y-3分子X-Y=6 3(X+Y)=4(X-Y) 老做不对,
2分子X+Y-3分子X-Y=6 3(X+Y)=4(X-Y) 老做不对,

2分子X+Y-3分子X-Y=6 3(X+Y)=4(X-Y) 老做不对,
(x+y)/2 -(x-y)/3 =6 (1)
3(x+y)=4(x-y) (2)
(1)等式两边同乘以6,得
3(x+y)-2(x-y)=36 (3)
(2)变形,得
3(x+y)-4(x-y)=0 (4)
(3)-(4)
2(x-y)=36
x-y=18 (5)
(3)×2-(4)
3(x+y)=72
x+y=24 (6)
(5)+(6)
2x=42 x=21
(6)-(5)
2y=6 y=3
x=21 y=3