%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-2-33 on page II-149 in "breqn --- Automatic line breaking in math displays".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3examargin}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{171.0pt}

%StartShownPreambleCommands
\usepackage{breqn}
%StopShownPreambleCommands

\begin{document}
\begin{dgroup*}
  \begin{dmath} (a+b)^2 = a^2+2ab+b^2 \end{dmath}
  \begin{dmath} (a-b)^2 = a^2-2ab+b^2 \end{dmath}
  \begin{dmath*} (a+b)(a-b) = a^2-b^2 \end{dmath*}
\end{dgroup*}
\begin{dmath}
  \frac{1}{x} \condition{for $x\ne 0$}
\end{dmath}
\end{document}
