I think that books in the context of LLM can be super useful.

The approach that works for me is using Justin's Skycak methods he mentions in his books:

https://www.justinmath.com/books/

Check the shorter "Advice on upskilling" or "The Math Academy way" for well researched approach.

Basically, using the books as the source for the LLM to limit itself by RAG-ing the text and then generate the required tests, questions and explanation of the concepts.