There are two ways to include mathematical formulae as inlines within a paragraph.

If your expressions are relatively simple, you can enclose them inside an element like this:

<phrase role='math'>…</phrase>

This will show all letters in italics. Here is an example:

We must prove that

afor all cases.^{2}<b_{x}

Here is the source for that example:

We must prove that <phrase role='math' >a<superscript >2</superscript ><b<subscript >x</subscript ></phrase > for all cases.