Why my jekyll site on github not work with mathjax? - github

Question

I start to build a jekyll site on github following this BLOG.
OK it works.
I would like to add some math stuffs in my blog, I add a "mathjax.html" in "include folder"
<script type="text/x-mathjax-config">
MathJax.Hub.Config({
TeX: {
equationNumbers: {
autoNumber: "AMS"
}
},
tex2jax: {
inlineMath: [ ['$','$'],
['\(', '\)'] ],
displayMath: [
['$$','$$'] ],
processEscapes:true,
}
});
and then include this file in Layouts files(default.html page.html post.html)
<div class="wrapper-footer">
<div class="container">
<footer class="footer">
{% include svg-icons.html %}
</footer>
</div>
</div>
{% include analytics.html %}
</body>
</html>
{% include mathjax.html %}
default.html
---
layout: default
---
{% include mathjax.html %}
<article class="page">
<h1>{{ page.title }}</h1>
<div class="entry">
{{ content }}
</div>
</article>
page.html
---
layout: default
---
<article class="post">
<h1>{{ page.title }}</h1>
<div class="entry">
{{ content }}
</div>
<div class="date">
Written on {{ page.date | date: "%B %e, %Y" }}
</div>
{% include disqus.html %}
</article>
{% include mathjax.html %}
post.html
and add this line in post file
$$ sin(x^2) $$
As a result ,the page show nothing ...
what 's wrong with it?