$\text { Đáp án: }$
$\left \{ {{5x+3y=19} \atop {x+y=5}} \right.$
` <=> ` $\left \{ {{5x+3y=19} \atop {x=5-y}} \right.$
` <=> ` $\left \{ {{5(5-y)+3y=19} \atop {x=5-y}} \right.$
` <=> ` $\left \{ {{25-5y+3y=19} \atop {x=5-y}} \right.$
` <=> ` $\left \{ {{2y=6} \atop {x=5-y}} \right.$
` <=> ` $\left \{ {{y=3} \atop {x=5-y}} \right.$
` <=> ` $\left \{ {{y=3} \atop {x=5-3}} \right.$
` <=> ` $\left \{ {{y=3} \atop {x=2}} \right.$
