# What are some common ways to add variable descriptions with equations? [closed]

I'm looking for a good way to add variable descriptions immediately following equations. In plain text, it might look something like this:

r_p = a(1-e)

where a is semi-major axis

(space) e is eccentricity (perhaps e is neatly aligned with a)

Further, I'm interested in placing this equation and the descriptions inside of a list:

\begin{itemize}
\item Periapse
\begin{itemize}
\item The point of closest approach to the foci
$r_p = a(1-e)$
(variable descriptions)
\end{itemize}
\item Apoapse
\begin{...
...
\end{itemize}


## closed as too broad by egreg, Svend Tveskæg, user13907, Mico, Przemysław ScherwentkeSep 11 '15 at 11:06

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

Like this?

% arara: pdflatex

\documentclass{article}
\usepackage{array}
\newcommand{\where}[1]{where~\begin{tabular}[t]{@{}>{$}c<{$}@{ }l@{}}#1\end{tabular}}

\begin{document}
\begin{itemize}
\item Periapse
\begin{itemize}
\item The point of closest approach to the foci
$r_p = a(1-e)$
\where{a & is semi-major axis \\e & is eccentricity}
\end{itemize}
\item Apoapse
\end{itemize}
\end{document}