I always feel kind of scared that I am violating a copyright law when I copy problems from textbooks in posts even though I always try to paraphrase. However, this is not really possible when it comes to equations and is not really feasible with the more intricate problems sometimes. Does anyone know what the copyright regulations are for problems in textbooks? Is it illegal to copy problems verbatim? Is it illegal to just scan the problem and attach it to your post instead of typesetting all of that LaTeX?