Slight rendering problem here: ``:math:`i`th``
You either need a space after `:math:'i'` but this will give `i th` with the space in between.
Else try a backslash `\` after the `:math:'i'`
Currently it makes a 
![image](http://i43.tinypic.com/1sl404.png)

Have a look if the backslash fixes the problem :)