%% 
%%  An UIT Edition example
%% 
%%  Example 06-02-5 on page 81.
%% 
%%  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[english]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{225.70511pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\setcounter{equation}{0}
\renewcommand\theequation{6.\arabic{equation}}
\StartShownPreambleCommands
\usepackage{amsmath}
\StopShownPreambleCommands
\begin{document}
\begin{align}
 y      &= d\\
 y      &= cx+d\\
 y_{12} &= bx^2+cx+d\\
 y(x)   &= ax^3+bx^2+cx+d
\end{align}
\end{document}