%% 
%%  An UIT Edition example
%% 
%%  Example 03-02-5 on page 18.
%% 
%%  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}
\setlength\parindent{0pt}
\setcounter{equation}{1}
\renewcommand\theequation{3.\arabic{equation}}
\StartShownPreambleCommands

\StopShownPreambleCommands
\begin{document}
\begin{minipage}{0.49\linewidth}
The line above the equation.

\[ f(x)=\prod_{i=1}^n\left(i-\frac{1}{2i}\right) \]

The line below the equation.
\end{minipage}\hfill\begin{minipage}{0.49\linewidth}
The line above the equation.

\begin{equation} f(x)=\prod_{i=1}^{n}\left(i-\frac{1}{2i}\right) \end{equation}

The line below the equation.
\end{minipage}
\end{document}