%% 
%%  Der Mathematiksatz mit LaTeX, 1. Auflage 2009
%% 
%%  Example 3-5-1 on page 26.
%% 
%%  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{355.65944pt}
\usepackage[utf8]{inputenc}
\setcounter{equation}{24}
\renewcommand\theequation{3.\arabic{equation}}\usepackage[ngerman]{babel}
\setlength\parindent{0pt}
\setlength\parskip{1ex plus 0.2ex}
\StartShownPreambleCommands

\StopShownPreambleCommands
\begin{document}
Ähnlich zum Zeilenmodus kann man auch abgesetzte Formeln einrahmen, allerdings
müssen \ldots

\fbox{\parbox{\linewidth}{%
\begin{equation}
  f(x)=\int_1^{\infty}\frac{1}{x^2}\,\mathrm{d}x=1
\end{equation}}}
\end{document}
