i thought i understand it but i guess i don't... you can expand a function in cosine f.s., sine f.s. and complete f.s. on some [0..L]. i thought that the coefficients a_n and b_n for complete expansion would come from sines and cosines respectively, but i guess that wouldn't make sense, since then your function will just double when expanded with complete f.s. can someone explain this point to me please.