予習 and 復習: preparation and review
Distinguish preparation before a lesson from reviewing what has been learned.
Preparing before a lesson
予習 (よしゅう) means studying material before it is taught. 「明日の授業を予習しました」 says that the speaker prepared for tomorrow's lesson, not that they already attended it.
「教科書を読んで予習します」 means preparing by reading the textbook. Reading is the method, while 予習 describes its role before the lesson.
Revisiting learned material
復習 (ふくしゅう) means reviewing material already learned. 「今日習った漢字を復習しました」 says that the speaker reviewed the kanji learned today.
「復習しても、まだ覚えられません」 means still being unable to memorize it despite review. Reviewing does not guarantee successful recall.
Identifying the reference lesson
「前の授業を復習してから、次の授業を予習しました」 describes reviewing the previous lesson and then preparing for the next. Both can occur in one study session.
Reading the same book can be preparation or review depending on whether the material has been taught. Focus on timing relative to the lesson rather than the book or tool.
Is all studying the day before a class 予習?
Show the answer and why
No. Revisiting previously learned material can be 復習. Check the material and reference lesson, not just the date.