%% 
%%  An UIT Edition example
%% 
%%  Example 03-02-3 on page 17.
%% 
%%  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{177.70511pt}
\setlength\parindent{0pt}
\usepackage[english]{babel}
\setcounter{equation}{0}
\renewcommand\theequation{3.\arabic{equation}}
\StartShownPreambleCommands

\StopShownPreambleCommands
\begin{document}
A normal line of text before the
\texttt{equation} environment.
%
\begin{equation}
 f(x)=\prod_{i=1}^{n}\left(i-\frac{1}{2i}\right)
\end{equation}
%
A normal line of text after the
\texttt{equation} environment.
\end{document}