I want to know how many levels of trigonometries there are in the world of math. Which one, in your opinion, is the toughest trigonometry course taught at the college level?
I think there is not much to learn about trigonometry (functions, properties...). But the applications of trigonometry are less easy to grasp. You can have a look here : Uses of trigonometry - Wikipedia, the free encyclopedia
I don't think there is a trigonometry course at my university lol.