Tính hệ pt .

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`d)`

`{(x-y=3),(3x-4y=2):}`

Từ `x-y=3=>x=y+3`

Thay `x=y+3` vào `3x-4y` :

`3(y+3)-4y=2`

`3y+9-4y=2-y+9=2`

`-y=2-9-y=-7`

`y=7`

`x=7+3=10`