Recently while answering a question I had to write an integral which was something like this. The problem here is the integral symbol looks too small. I went through the mathjax tutorial in this meta thread but couldn't find how to make this integral larger.
$$\int\frac{\left(\sqrt{(3u^2+1)^2-2u^2}\right)}{2\sqrt{u}}\,du$$
Any references to a broader $\TeX$ tutorial besides this specific question would be very helpful.