Paper is paper. Airport security won't find a piece of hand-written paper inside a book because they aren't looking for it. They are almost exclusively concerned with weapons, and paper isn't a weapon. They don't even want to find things like narcotics - not their job and it requires lots of police paperwork. Similarly, they are spectacularly uninterested in the contents of your computer.
Now, that's security getting on the plane. If you are talking about Customs and Immigration after you get off the plane, that's a different story. If you have come to the attention of C&I, the folded paper will be of interest and will be read. If it's homework on the textbook topic, no problem. If it's building plans to a national monument you should expect to miss your connecting flight.