equation numbering in html and latex export

[Samuel Sinayoko <s.sinayoko@soton.ac.uk>]

Dear list,

I've been trying to write short scientific reports that I can export to
both LaTeX and HTML. So far I've managed to figure out how to include
equations, images, references, and how to include labels and cross
reference between all these things.

The only problem I have is that I can't get numbered equations in both
LaTeX and HTML. Using the snippet below, I'm able to get a numbered
equation in HTML but not in LaTeX. I've put
loadFiles: ["extensions/eqn-number.js"], 
in jsMath/easy/load.js. If I replace the $$ by
\begin{equation} and \end{equation}, I get a numbered equation in LaTeX
but not in HTML. 

How can I get numbered equations in both HTML and LaTeX?

Thanks,

Sam

-------
#+TITLE: A simple equation
#+STYLE: <SCRIPT SRC="jsMath/easy/load.js"></SCRIPT>
#+OPTIONS: LaTeX:verbatim
* A simple equation
This is to test writing equations with org-mode. Hopefully MathJax is going to be used.
$$
\label{eq:1}
 x_{1,2} = \frac{-b \pm \sqrt{\Delta}}{2a} 
$$
Equation \ref{eq:1} gives the roots of a polynomial of order 2.