# [texhax] Simultaneous Equations?

E. Krishnan ekmath at md5.vsnl.net.in
Wed Feb 18 06:43:26 CET 2004

On Thu, 12 Feb 2004, Gavin Baker wrote:

> I just want two numbered equations, with one { to the left of them.
> I'm using LaTeX.

Here's a somewhat crude methosd I used to get numbered "cases" in
equations, which is similar to your requirements.

\usepackage{amsmath}
\usepackage{calc}

\newenvironment{ncases}[4]{%
\parbox{\textwidth-2cm}{%
\begin{equation*}
#1=
\begin{cases}
#2
\end{cases}
\end{equation*}}
\hfill
\parbox{1cm}{%
\begin{eqnarray}
{}\label{#3}\\
{}\label{#4}
\end{eqnarray}}}

\begin{document}

\begin{ncases}
{|x|}{x, &\text{if $x\ge 0$}\\
-x,&\text{if $x\le 0$}}{pos}{neg}
\end{ncase}

From this it easily follows that
$$|x|\ge0\;\text{for all x\in R}$$
for if $x\ge 0$, then by Equation~\eqref{pos}, we have $|x|=x\ge0$ and
if $x\le0$, then by Equation~\eqref{neg}, we have $|x|=-x\ge0$.

--
Krishnan