Verified answer

[tex]1.[/tex]

[tex]\left \{ {{x - 2y = 3} \atop {5x + y = 4}} \right. \\ [/tex]

x-2y=3 → x=3+2y

Вместо х поставим выражение

[tex]5x + y = 4 \\ 5(3 + 2y) + y = 4 \\ 15 + 10y + y = 4 \\ 10y + y = 4 - 15 \\ 11y = - 11 \\ y = - 1[/tex]

[tex]x = 3 + 2y \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \\ x = 3 + 2 \times ( - 1) = 3 - 2 = 1[/tex]

[tex]2.[/tex]

[tex]\left \{ {{3x - 2y = 15} \atop {4x + 2y = 6}} \right. + \\ 7x = 21 \\ x = 3 \\ \\ 4x + 2y = 6 \\ 4 \times 3 + 2y = 6 \\ 12 + 2y = 6 \\ 2y = 6 - 12 \\ 2y = - 6 \\ y = - 3[/tex]