%% 
%%  An UIT Edition example
%% 
%%  Example 03-05-3 on page 26.
%% 
%%  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}
\usepackage[utf8]{inputenc}
\setcounter{equation}{27}
\renewcommand\theequation{3.\arabic{equation}}\setlength\parskip{1ex plus 0.2ex}
\StartShownPreambleCommands

\StopShownPreambleCommands
\begin{document}
\begin{equation}
  f(x)=\int_1^{\infty}\frac{1}{x^2}\mathrm{d}x=1
\end{equation}\renewcommand*\theequation{*}
%
\begin{equation}\label{eq:*}
  f(x)=\int_1^{\infty}\frac{1}{x^2}\mathrm{d}x=1
\end{equation}
%
When we want to refer to the equation labelled with a star we use
\verb+\ref{eq:*}+ in the coding and this results in
\ref{eq:*} --- the star is output correctly in the text.
\end{document}