Geometry refresher needed!

I think you are skipping over parts of the math too quickly. I don’t know what x'(1,0) or y'(0,1) even means or why you chose them.

It took me a while to scrape the rust off my basic math skills in order to follow the presentation. A few days later I realised that using the value of 1 for the hypotenuse on the x’ y’ axes provides a template that can be scaled up to solve a translation problem – once we are given a value for the angle of rotation (theta), and the coordinates to be translated . . . but it was a slow, grinding process that only resolved at 3am after several days and nights of careful consideration 🙂