Ennis has had it explained to her that, while you don't need to do your own homework, you do need to look alive enough during class that you will not die the death of a thousand papercuts if anything should befall the person who is doing your homework. It doesn't even have to be a fatal befalling; they could fail to understand the material or get sick or something. So she needs to actually contact the concepts in Advanced Geometry enough that during any given week she can cover her own assignments if taken by surprise.

Advanced Geometry is going to involve a lot of proofs, apparently. Ennis reads about proofs once she's found her textbook.