$\left \{ {{5x-4y=3} \atop {2x+y=4}} \right.$
⇔ $\left \{ {{5x-4y=3} \atop {8x+4y=16}} \right.$
⇔ $\left \{ {{13x=19} \atop {5x-4y=3}} \right.$
⇔ $\left \{ {{x=\frac{19}{13}} \atop {5.\frac{19}{13}-4y=3}} \right.$
⇔ $\left \{ {{x=\frac{19}{13}} \atop {4y=\frac{56}{13}}} \right.$
⇔ $\left \{ {{x=\frac{19}{13}} \atop {y=\frac{14}{13}}} \right.$
Vậy phương trình có nghiệm duy nhất (x ; y) = (`\frac{19}{13};\frac{14}{13}`)
