Given:
$ e^{2jt}\! $ through a system produces $ e^{-2jt}\! $, and $ e^{-2jt}\! $ produces $ e^{2jt}\! $. what is the output of $ cos(2t)\! $
$ cos(2t)\! $ can also be written as $ (e^{2jt} + e^{-2jt})/2\! $
