In the following sentence:
深入 is a verb, and 学习 is also a verb or noun. So it is awkward 学习 modifies a verb here.
One possibility is that 的 is misspelled with 得 here and 深入 is used an an adjective (meaning "thorough" or "deepgoing"), but this text is formal and not something you see on the web (it is a textbook for Chinese learners).
So why is 的 used in such a way? What does it mean here, and is it grammatically correct? Or is it simply a typo with 得 (which sometimes happen among native Chinese speakers, though as I said, it is a textbook for language learners and should be checked before pubilshed)?