I am attaching the article that I use in class. My students read parts of it before we start these problems. I was just going to link to it but for some reason it is surprisingly hard to find online. I’m glad I have a copy – here it is:
The author of the article – Tony Rothman – also has a book called “Sacred Mathematics: Japanese Temple Geometry” that covers Sangaku and can be found here:
I will write about the pedagogy a different day – but if you are interested in these problems I wanted to share the article above.