See the thread https://www.physicsforums.com/showthread.php?t=386951
Basically, say you want to display [itex]\sqrt{2}[/itex]. Then you need to find the correct formula for sqrt, and that is \sqrt{...} and then you need to type it between [ itex ] ... [ /itex] tags (without spaces).
Thus, we should type [ itex ]\sqrt{2}[ /itex ].