\scalebox{0.97}{
$\og{
\hspace{-0.75cm}
\arraycolsep=0cm
\left\{
\begin{array}{rrrrr rrrrr rrrrr rrrrr rrrrr rr}
a_{1\,1}x_{1} & + & a_{1\,2}x_{2} & + & \ldots & + & a_{1\,i-1}x_{i-1} & + & a_{1\,i}x_{i} & + & a_{1\,i+1}x_{i+1} & + & \ldots & + & a_{1\,j-1}x_{j-1} & + & a_{1\,j}x_{j} & + & a_{1\,j+1}x_{j+1} & + & \ldots & + & a_{1\,n-1}x_{n-1} & + & a_{1\,n}x_{n} & = & b_{1} \\
a_{2\,1}x_{1} & + & a_{2\,2}x_{2} & + & \ldots & + & a_{2\,i-1}x_{i-1} & + & a_{2\,i}x_{i} & + & a_{2\,i+1}x_{i+1} & + & \ldots & + & a_{2\,j-1}x_{j-1} & + & a_{2\,j}x_{j} & + & a_{2\,j+1}x_{j+1} & + & \ldots & + & a_{2\,n-1}x_{n-1} & + & a_{2\,n}x_{n} & = & b_{2} \\
\hdotsfor{27}\\
a_{k-1\,1}x_{1} & + & a_{k-1\,2}x_{2} & + & \ldots & + & a_{k-1\,i-1}x_{i-1} & + & a_{k-1\,i}x_{i} & + & a_{k-1\,i+1}x_{i+1} & + & \ldots & + & a_{k-1\,j-1}x_{j-1} & + & a_{k-1\,j}x_{j} & + & a_{k-1\,j+1}x_{j+1} & + & \ldots & + & a_{k-1\,n-1}x_{n-1} & + & a_{k-1\,n}x_{n} & = & b_{k-1} \\
a_{k\,1}x_{1} & + & a_{k\,2}x_{2} & + & \ldots & + & a_{k\,i-1}x_{i-1} & + & a_{k\,i}x_{i} & + & a_{k\,i+1}x_{i+1} & + & \ldots & + & a_{k\,j-1}x_{j-1} & + & a_{k\,j}x_{j} & + & a_{k\,j+1}x_{j+1} & + & \ldots & + & a_{k\,n-1}x_{n-1} & + & a_{k\,n}x_{n} & = & b_{k} \\
\hdotsfor{27}\\
\end{array}
\right.
}$
}
Сначала я написал следующую новую команду (только не смейтесь) ):