After a long break from math I started taking another crack at it. I'm not sure I'll ever get to this graphical stuff, but I'm sorting through a trigonometry link.
https://www.raywenderlich.com/35866/trigonometry-for-game-programming-part-1
What is getting me is that you need to know something about the triangle to deduct the information. How do you gather intel, if you don't know anything about it.
Two sprites on the screen, you have no idea what points they're at. How on earth do you do trigonometry with a blank triangle?