[tex]1)\left\{\begin{matrix}
x - 2y = 0& \\
4x + 5y = 26&
\end{matrix}\right.[/tex]
[tex]x - 2y = 0 = > x = 2y[/tex]
[tex]4x + 5y = 26[/tex]
[tex]4 \times 2y + 5y = 26[/tex]
[tex]8y + 5y = 26[/tex]
[tex]13y = 26 \: | \div 13[/tex]
[tex]y = 2[/tex]
[tex]x = 2y = > x = 2 \times 2 = 4[/tex]
[tex]2)\left\{\begin{matrix}
4x - 7y = 30& \\
4x - 5y = 90 \: | \times ( - 1) &
\end{matrix}\right.[/tex]
[tex]\left\{\begin{matrix}
4x - 7y = 30& \\
- 4x + 5y = - 90&
\end{matrix}\right.[/tex]
[tex] - 2y = - 60 \: | \div ( - 2)[/tex]
[tex]y = 30[/tex]
[tex]4x - 7y = 30[/tex]
[tex]4x - 7 \times 30 = 30[/tex]
[tex]4x - 210 = 30[/tex]
[tex]4x = 30 + 210[/tex]
[tex]4x = 240 \: | \div 4[/tex]
[tex]x = 60[/tex]
