Изменения

<tex> \begin{vmatrix} x_3 \\ x_4 \\ x_5 \\ x_7 \end{vmatrix} = \begin{vmatrix} 0 & 0 & 1 & 0 \\ 0 & 0 & 0 & 1 \\ a_{51} & a_{52} & a_{53} & a_{54} \\ a_{71} & a_{72} & a_{73} & a_{74} \end{vmatrix} = \begin{vmatrix} a_{51} & a_{52} \\ a_{71} & a_{72} \end{vmatrix} =0 </tex>

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