$$\left[\begin{array}{cc}1& 2\\ 3& 4\end{array}\right]\left\{\begin{array}{c}ax+by=c\\ ex+fy=g\end{array}\right.$$ $$\left|\begin{array}{ccc}1& \mathrm{\dots }& a_{1\mathrm{n}}\\ \mathrm{⋮}& \mathrm{\ddots }& \mathrm{⋮}\\ a_{\mathrm{n}1}& \mathrm{\dots }& 1\end{array}\right|\begin{array}{|ccc|}\hline 1& 2& 3\\ 1& 2& 3\\ 1& 2& 3\\ \hline\end{array}$$

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