For the most part, the TeX Notation has been built using a sub-set of characters from the TeX “default” character set. The trouble is there does not seem to be a “default” character set for TeX. This is one of the most confusing aspects of using TeX Notation in Moodle. When we realise that the documentation we are using is related to the creation of printed documents, and we want to use TeX on line, in Moodle, then further problems occur. There are no environment statements to be made. There are few \begins and \ends. If you go to Administration > Modules > Filters > Filter Manager you will see what filters have been enabled. If you then go to the TeX Notation page, the default preamble is editable via the text box. Using this tool you can add in or subtract font packages and other packages, change the default font package, etc.

Source: Using TeX Notation – MoodleDocs