%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-2-12 on page II-138 in "Equation groups with simple 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}
% Shorten the vertical size of the example ...
\AtBeginDocument{%
\setlength\abovedisplayskip{.7\abovedisplayskip}%
\setlength\belowdisplayskip{.7\belowdisplayskip}%
}
%StartShownPreambleCommands
\usepackage{amsmath}
%StopShownPreambleCommands
\begin{document}
\begin{align}
(a + b)^3 &= (a + b) (a + b)^2 \\
&= (a + b)(a^2 + 2ab + b^2) \\
&= a^3 + 3a^2b + 3ab^2 + b^3
\end{align}
\begin{align}
x^2 + y^2 & = 1 \\
x & = \sqrt{1-y^2}
\end{align}
\end{document}
