$\text { Đáp án: }$
$\left \{ {{x+y=5} \atop {5x+2y=19}} \right.$
` <=> ` $\left \{ {{y=5-x} \atop {5x+2y=19}} \right.$
` <=> ` $\left \{ {{y=5-x} \atop {5x+2(5-x)=19}} \right.$
` <=> ` $\left \{ {{y=5-x} \atop {5x+10-2x=19}} \right.$
` <=> ` $\left \{ {{y=5-x} \atop {5x-2x=19-10}} \right.$
` <=> ` $\left \{ {{y=5-x} \atop {3x=9}} \right.$
` <=> ` $\left \{ {{y=5-x} \atop {x=3}} \right.$
` <=> ` $\left \{ {{y=5-3} \atop {x=3}} \right.$
` <=> ` $\left \{ {{y=2} \atop {x=3}} \right.$
$\text { Vậy }$ $\left \{ {{y=2} \atop {x=3}} \right.$
