%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-2-7 on page II-135 in "A single equation on several lines: with 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{equation}
  \begin{split}
   (a + b)^4
     &= (a + b)^2 (a + b)^2      \\
     &= (a^2 + 2ab + b^2)
        (a^2 + 2ab + b^2)        \\
     &= a^4 + 4a^3b + 6a^2b^2 + 4ab^3 + b^4
  \end{split}
\end{equation}
\end{document}