%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-2-10 on page II-137 in "Equation groups without alignment".
%%
%% 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{207.0pt}

%StartShownPreambleCommands
\usepackage{amsmath}
%StopShownPreambleCommands

\begin{document}
\begin{gather}
  (a + b)^2 = a^2 + 2ab + b^2          \\
  (a + b) \cdot (a - b) = a^2 - b^2
\end{gather}
\end{document}
