First method

I googled this site helps to make LaTeX working in blogspot. I have prosseek/files, for file storing purposes (even though it allows me keep only 1GB). Just right click in google/sites, and copy the file using HREF allows me to download the file from the site like this.
The code is as follows:
$latex \displaystyle S(n)=\sum_{k=1}^{n}{\frac{1}{T_{k}}=\sum_{k=1}^{n}{\frac{6}{k(k+1)(k+2)}$

This is the result: $latex \displaystyle S(n)=\sum_{k=1}^{n}{\frac{1}{T_{k}}=\sum_{k=1}^{n}{\frac{6}{k(k+1)(k+2)}$
You can refer to this post for embedding HTML/javascript in your blog.

MathJax

I googled this post to use MathJax. You need to add the code in template, which add jQuery and MathJax.


MathJax.Hub.Config({
extensions: ["tex2jax.js","TeX/AMSmath.js","TeX/AMSsymbols.js"],
jax: ["input/TeX", "output/HTML-CSS"],
tex2jax: {
inlineMath: [ ['$','$'], ["\$","\$"] ],
displayMath: [ ['$$','$$'], ["\$","\$"] ],
},
"HTML-CSS": { availableFonts: ["TeX"] }
});


The code is as follows:
$x + y_3$


And this is the result: $x + y_3$

Warning

As is written in this post, there is a bug that the result is not shown in Chrome.