I was contacted by professor Wildberger last week regarding a series of YouTube videos introducing rational trigonometry. This is a new way of thinking about trigonometry and Euclidean geometry that I find rather interesting. I’ve always been intrigued with new ways of looking at foundational topics.
So, if you’re confused about those pesky circular functions like sine and cosine or just want to check out something new and interesting (especially if you teach math), then check out this video,
WildTrig0: An Invitation to geometry: the WildTrig series
Links to the entire series of videos are provided here and this is Dr. Wildberger’s personal site.
The Algorithmist 
I’ll have to ask my profs at school about this. Some of it was over my head 🙂