$ e^{2jt} --> system --> te^{-2jt} $ $ e^{-2jt} --> system --> te^{2jt} $
=>$ \cos(2t) $ --> system =$ \frac{e^{2jt}+e^{-2jt}}{2} $ --> system =$ \frac{1}{2}(e^{2jt}+e^{-2jt}) $ -->system
