You can use the align
environment if you want. Remove the *
to get the numbered equation form. The following is MWE:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align*}
A {}={} & B + C + D + E + F +\\
& G + H + I + \dotsb, \quad \text{while $x$ is true.}
\end{align*}
\end{document}
Another flavor would be like:
\[
\begin{aligned}
A {}={} & B + C + D + E + F +\\
& G + H + I + \dotsb, \quad \text{while $x$ is true.}
\end{aligned}
\]
or
\[
\begin{array}{r@{}c@{}l}
A &{}={}& B + C + D + E + F +\\
& & G + H + I + \dotsb, \quad \text{while $x$ is true.}
\end{array}
\]
This does not give any numbered version but keeps the alignment. I recommend you read the amsmath
documentation and other math related sources to get acquainted with alignments in equations. For example, here in TeX.SX you can make a quick search and you will see several examples of alignment. For instance if I search alignment in equations
I would get lots of examples. (click me)
I will also invite you to read the following links:
- https://tex.stackexchange.com/a/147149/10898
- https://tex.stackexchange.com/a/122497/10898
align
orarray
environment.