school/uni textbooks? Depends which ones you want but I usually try ResearchGate. I get the name of the textbook/article/etc then write into a search bar that name plus ResearchGate and it usually comes up with a free copy. Sometimes you can just google the textbooks name and see if anyones been kind enough to put a free version up.

https://www.pdfdrive.com/
I found this quite helpful

Thanks guys. I'll try those and hopefully find the books I need

What books are you specifically looking for? Maybe we can help

A. Barnett, Raymond; Ziegler, Michael & E. Byleen, Karl (2015) College Mathematics for Business, Economics, Life Sciences, and Social Sciences. Prentice Hall, NJ.