I can see that the posts on this site contain nicely displayed mathematical formulas. How can I get such formulas in my posts? What syntax is used to typeset them?
Note: This is an attempt to make at least brief overview of MathJax syntax available directly here on MO - as suggested some time ago in this answer: FAQ on typesetting of formulae hard to find. (Perhaps this post also supports the idea that something like this might be useful: Quickly Accessible MathJax Help.) The question and answers are community wiki in order to encourage collaborative editing. We should probably try to keep the tutorial simple and brief - with links to other resources, in case somebody needs more details.