Resources for Geometry / Trigonometry

The book has been great so far, thank you for the effort. I’m on chapter 4 (Drawing custom component), which is math heavy (but at the same time interesting). Could you please recommend some resources for those geometry/trigonometry calculations? (I would like to learn, to come by my own with those values)

A simple search for each (geometry or trig) reveals lots of content, and in several media formats. I would personally just got back to basics, as a solid foundation lets you build and understand everything better.