Regarding LaTeX formatting and recognized symbols, one suggestion is to try typing what you want into the Desmos Graphing Calculator and see if you can type an expression without any errors popping up. For example, if I type in ∠M=20, an error pops up reading, “Sorry, I don’t understand the ‘∠’ symbol.” If the Graphing Calculator does not support a particular notation, you can expect that CL also does not.
If you can type an expression without any errors, then copying and pasting it from the calculator into CL will automatically convert it into LaTeX (e.g. copying an inverse function will give you the LaTeX that @pirsquared provided).
@sergeballif shared some great explanation in this thread of why LaTeX use is limited in Desmos.
One last note - one useful resource for teaching yourself CL is the official documentation.