However, the opinions expressed here are my own and I am not speaking for Ao PS.] The Ao PS subject books (Prealgebra, Introduction to Algebra, etc) are meant to be stand-alone textbooks which you can learn from without using another textbook.
Both the problem itself and the more advanced theorem from “Geometry Revisited” that it hinted at were super fun to talk through with my son.
Here’s us doing a quick review of the problem itself tonight: The Art of Problem Solving problems are so great to begin with and it is sort of doubly fun to be able to use them as stepping stones to show some more advanced geometry.
Next up for us is the section on perimeter and area.
I just acquired the art of problem solving prealgebra book.