Ответ:

[tex]\left \{ {{x=2y} \atop {5x+3y=26}} \right.[/tex]

[tex]\left \{ {{x=2y} \atop {5*2y+3y=26}} \right.[/tex]

5*2y+3y=26

10y+3y=26

13y=26

y=26 : 13

y= 2

[tex]\left \{ {y=2} \atop {x=2*2}} \right.[/tex]

x=2*2

x=4

[tex]\left \{ {{x=4} \atop {y=2}} \right.[/tex]

Ответ: (4 ; 2)