How can I have linebreaks in my long LaTeX equations?

Question

My equation is very long. How do I get it to continue on the next line rather than go off the page?

Answer 1

Not yet mentioned here, another choice is environment aligned, again from package amsmath:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{equation}
  \begin{aligned}
    A & = B + C\\
      & = D + E + F\\
      & = G
  \end{aligned}
\end{equation}

\end{document}

This outputs: