This one uses a Javascript to load MathJax direct. Seems easier than the plug-in.
In equation 1, we find the value of an
interesting integral:
$$\int_0^\infty \frac{x^3}{e^x-1}\,dx = \frac{\pi^4}{15}$$
or this:
\(\int_0^\infty \frac{x^3}{e^x-1}\,dx = \frac{\pi^4}{15}\)
or this:
$$\mathcal{\int_0^\infty \frac{x^3}{e^x-1}\,dx = \frac{\pi^4}{15}}$$