MaxJax is an open-source JavaScript display engine for LaTeX, MathML, and AsciiMath notation that works in all modern browsers.

1) Add the MathJax script from cdn into your HTML. I use the TeX syntax but you can also use mathML by including it in the config parameter.

<script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS_HTML"></script>

2) Change the default inline math delimiters of \(...\) as the brackets mean something else in markdown.

<script type="text/x-mathjax-config">
  MathJax.Hub.Config({
    extensions: ["tex2jax.js"],
    jax: ["input/TeX", "output/HTML-CSS"],
    tex2jax: {
      inlineMath: [ ['$','$']],
      displayMath: [ ['$$','$$']],
      processEscapes: true
    },
    "HTML-CSS": { availableFonts: ["TeX"] }
  });
</script>

So, $$ y = mx + b $$ appears on a new line:
$$ y = mx + b $$

and $y= mx + b$ appears inline: $y = mx + b$

3) Enjoy math scripting with TeX!
Here are some TeX samples