We know that:
$ \ e^{2jt} \rightarrow SYSTEM \rightarrow te^{-2jt} $
$ \ e^{-2jt} \rightarrow SYSTEM \rightarrow te^{2jt} $
We also know that the response for
$ \ cos(2t) = \frac{e^{2jt} + e^{-2jt}}{2} $
