To see how to incorporate LaTeX commands into comments, click here.
$latex\int f(x) dx =g$ produces the following equation (actually, you need to add a space after latex; I removed the space so that it would not be parsed as a LaTeX command).
or, to control the font size use $latex\int f(x)dx = g&s=-2$ to generate . The default font size is the same as s = 0. I use s=-2 for inline equations, and s=0 for stand alone equations. There is no equation mode, only in-line math mode. The preview option should allow you to check your syntax.