[tex]\left\{\begin{matrix}
x + 5y + 3 = 0\\
x - 2y - 4 = 0\end{matrix}\right.[/tex]
[tex]\left\{\begin{matrix}
x + 5y = - 3 \: | \times ( - 1) \\
x - 2y = 4\end{matrix}\right.[/tex]
[tex]\left\{\begin{matrix}
- x - 5y = 3\\
x - 2y = 4\end{matrix}\right.[/tex]
[tex] - 5y - 2y = 3 + 4[/tex]
[tex] - 7y = 7 \: | \div ( -7 )[/tex]
[tex]y = - 1[/tex]
[tex]x - 2y = 4[/tex]
[tex]x - 2 \times ( - 1) = 4[/tex]
[tex]x + 2 = 4[/tex]
[tex]x = 4 - 2[/tex]
[tex]x = 2[/tex]
[tex]\left\{\begin{matrix}
2x + 7y = 3\\
4x - y = - 9 \: | \times 7 \end{matrix}\right.[/tex]
[tex]\left\{\begin{matrix}
2x + 7y = 3\\
28x - 7y = - 63\end{matrix}\right.[/tex]
[tex]2x + 28x = 3 - 63[/tex]
[tex]30x = - 60 \: | \div 30[/tex]
[tex]x = - 2[/tex]
[tex]4x - y = - 9[/tex]
[tex]4 \times ( - 2) - y = - 9[/tex]
[tex] - 8 - y = - 9[/tex]
[tex] - y = - 9 + 8[/tex]
[tex] - y = - 1 \: | \times ( - 1)[/tex]
[tex]y = 1[/tex]
[tex]\left\{\begin{matrix}
3x - 2y - 9=0 \\
x + y - 8 = 0\end{matrix}\right.[/tex]
[tex]\left\{\begin{matrix}
3x - 2y = 9\\
x + y = 8 \: | \times 2 \end{matrix}\right.[/tex]
[tex]\left\{\begin{matrix}
3x - 2y = 9\\
2x + 2y = 16\end{matrix}\right.[/tex]
[tex]3x + 2x = 9 + 16[/tex]
[tex]5x = 25[/tex]
[tex]x = \frac{25}{5} [/tex]
[tex]x = 5[/tex]
[tex]x + y = 8[/tex]
[tex]5 + y = 8[/tex]
[tex]y = 8 - 5[/tex]
[tex]y = 3[/tex]
