%% 
%%  An UIT Edition example
%% 
%%  Example 03-06-4 on page 29.
%% 
%%  Copyright (C) 2010 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.
%% 
%% 
%% ==== 
% Show page(s) 1
%% 
\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{375.57637pt}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\setlength\parindent{0pt}
\setlength\parskip{1ex plus 0.2ex}
\StartShownPreambleCommands
\usepackage{varwidth}
\usepackage{calc}
\StopShownPreambleCommands
\begin{document}
Similar to inline mode, displayed formulae can be framed, but have to be \ldots
(This text is to illustrate the line width.)
\begin{center}
\fbox{\begin{varwidth}{\linewidth-2\fboxsep-2\fboxrule}
\[ f(x)=\int\limits_1^{\infty}\frac{1}{x^2}\,\mathrm{d}x=1 \]
\end{varwidth}}

\fbox{\begin{varwidth}{\linewidth-2\fboxsep-2\fboxrule}
\[ f(x)=\int\limits_1^{\infty}\frac{1}{x^2}\,\mathrm{d}x=1 \]
\vspace{\belowdisplayshortskip}
\end{varwidth}}
\end{center}
\end{document}