I am currently working through Linear Algebra: A Modern Introduction (by David Poole). It's going okay, but there are only half of the answers to the exercises in the book. For the most part I can get through the questions and be fairly confident in my answer without the need for an answer key. However, there are certain questions that I find extremely difficult and at times cannot solve. Would it be beneficial to purchase an answer key, so I can find out how to approach the problems I am stuck on? I am hesitant to purchase it as I don't want to waste money on something that isn't necessary. However, if it would help me better understand the material by having it I would buy it. Another thing is, I tend to skip or get help for questions I am stuck on for more than a day. Would it be better to keep working on these problems until I get them, even if it takes me a long time, or should I just move on.