Combinatie
\(\left\{\begin{matrix}-9x+3y=-57\\6x-9y=-18\end{matrix}\right.\)
\(\left\{\begin{matrix}-9x+3y=-57\\6x-9y=-18\end{matrix}\right.\\ \Leftrightarrow \left\{\begin{array}{c|c|c}-9x+3y=-57& \color{red}{2.} & \color{blue}{3.} \\6x-9y=-18& \color{red}{3.} & \color{blue}{1.} \end{array}\right.\\ \Leftrightarrow \left\{\begin{matrix} \color{red}{\underline{-18x+18x}+6y-27y=-114-54} \\ \color{blue}{-27x+6x\underline{+9y-9y}=-171-18} \end{matrix}\right.\\ \Leftrightarrow \left\{\begin{matrix}-21y=-168 \\-21x=-189\end{matrix}\right.\\ \Leftrightarrow \left\{\begin{matrix}y=\frac{-168}{-21}=8 \\x=\frac{-189}{-21}=9\end{matrix}\right.\\ \qquad V=\{(9,8)\}\)