%% 
%%  Der Mathematiksatz mit LaTeX, 1. Auflage 2009
%% 
%%  Example 4-8-9 on page 56.
%% 
%%  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{194.59192pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\StartShownPreambleCommands

\StopShownPreambleCommands
\begin{document}
$\begin{array}{rcl}
  y & = & d\\
  y & = & c\frac{1}{x}+d\\
  y & = & b\frac{1}{x^{2}}+cx+d
\end{array}$
{\renewcommand\arraystretch{2}% lokal halten
$\begin{array}{rcl}
  y & = & d\\
  y & = & c\frac{1}{x}+d\\
  y & = & b\frac{1}{x^{2}}+cx+d
\end{array}$}
\end{document}