Book problem


I am tying to create a book in opengl. I want to make it so the book turns pages. My problem is that I can’t quiet figure out the math for how the pages will turn so that they turn normaly(fall on top of each other). My pages will go through each other to go to their original position only on the other side of x-axis. Does anyone now of an equation to keep my pages flipping correctly?

right now I am using the sin and cosine functions but like I said it would just make the pages rotate to the other side, going through all the other pages

All replies are greatly appreciated