Well there are lots of creative writing forums. Even the base has litterary secotions. Mathmatics I cant help you with. Just about every forum for creative or liberal arts works has a literary section. I.E. Mangas, arts, Books. But math is more difficult.
Personally I like physicsforums (they also do math), chegg, or simply yahoo answers. What type of math? If it's a higher math like calc, differential equations, or linear algebra, I'd stick with physicsforums.