%% 
%%  Der Mathematiksatz mit LaTeX, 1. Auflage 2009
%% 
%%  Example 10-10-1 on page 236.
%% 
%%  Copyright (C) 2009 Herbert Voss
%% 
%%  It may be distributed and/or modified under the conditions
%%  of the LaTeX Project Public License, either version 1.3
%%  of this license or (at your option) any later version.
%% 
%%  See http://www.latex-project.org/lppl.txt for details.
%% 

\documentclass[]{ttctexa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{170.59192pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\StartShownPreambleCommands
\usepackage{amsmath}
\StopShownPreambleCommands
\begin{document}
\begin {align*}
  4x+  6y -2z &= -4\\
   x   -y +2z &= 9 \\[-1.4 ex]%
                   \cline{1-2}
  5x + 5y     &= 5 \\
   x + y      &= 1 \\[-1.4 ex]%
\multispan 2 {%
  \leaders\hbox{$\mkern-2mu\Relbar\mkern-2mu$}\hfil}\\
            y &= 1-x
\end {align*}
\end{document}