Bạn tham khảo:
$\left \{ {{2x-3y=1} \atop {x-4y=-7}} \right.$
⇔$\left \{ {{2x-3y=1} \atop {2x-8y=-14}} \right.$
⇔$\left \{ {{5y=15} \atop {2x-3y=1}} \right.$
⇔$\left \{ {{y=3} \atop {2x-3.3=1}} \right.$
⇔$\left \{ {{y=3} \atop {x=5}} \right.$
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