MathJax has been enabled on this instance. To use to display a LaTeX expression inline, simply wrap it in dollar signs (e.g., $E=mc^2$ will appear as E=mc^2). If you wish put the expression on it’s own line and center it wrap it in double dollar signs like this:
$$
\int_0^1 f(x)v(x) \, dx = \int_0^1 u''(x)v(x) \, dx
$$
Which will appear as
\int_0^1 f(x)v(x) \, dx = \int_0^1 u''(x)v(x) \, dx
You may also want to use asciimath input by wrapping it in percent signs (i.e., %) instead.