For a test, I installed plugins, which offer MathJax support on a WordPress site. The first one was MathJax-LaTeX. It worked okay, but did not understand \dfrac, which sets fractions in display size. So I tried LaTeX for WordPress. In contrast to the Jetpack solution, it sets the formula with JavaScript. This will not work, if JavaScript is disabled or on old browsers. And the site update is no longer immediate on weak devices.

However, the font size now looks okay on my Nexus 7; maybe a bit tiny but readable.

\(\int\limits_a^b t^4 \, dt = \dfrac{b^5-a^b}{5} \)

To get the rest of the blog to work, I had to edit the JavaScript code. I used $latex for formatting, but the plugin expects $$. This can be fixed by changing the regexp variable in the code.

By the way, if you need a $ sign in the blog you have to enter it as $ in text (not visual) mode. You have to redo that on any update, since the WordPress editor changes your careful dollar signs to simple Unicode dollars.