$\left \{ {{2x+y=8} \atop {x-3y=-4}} \right.$
⇔$\left \{ {{y=8x-2} \atop {x-3y=-4}} \right.$
⇔$\left \{ {{y=8-2x} \atop {x-3(8-2x))=-4}} \right.$
⇔$\left \{ {{y=8-2x} \atop {x-24+6x=-4}} \right.$
⇔$\left \{ {{y=8-2x} \atop {7x=20}} \right.$
⇔$\left \{ {{y=8-2x} \atop {x=\frac{20}{7}}} \right.$
⇔$\left \{ {{y=8-2.\frac{20}{7}} \atop {x=\frac{20}{7}}} \right.$
⇔$\left \{ {{y=\frac{16}{7}} \atop {x=\frac{20}{7}}} \right.$
Nếu thấy có ích hãy cho mình 5 sao và ctlhn.
