How to write math symbols in khan academy?

Normally, when I do math problems in Khan Academy, I often get annoyed with having to open the toolbar and type characters (x,y,z,m,n,...) from there. That takes me a lot of time to do the problem. Well, sometimes just pressing it will naturally produce characters, but most of the time it is just normal letters and the results with those characters are not accepted. Can anyone tell me how to always enter math characters like x,y,z? Or how to make Khan Academy recognize normal letters?