$ x_1(t) = e^{2jt} \rightarrow $ Linear System $ \rightarrow y_1(t) = te^{-2jt} $
$ x_2(t) = e^{-2jt} \rightarrow $ Linear System $ \rightarrow y_2(t) = te^{2jt} $
With an input of $ cos(2t) $, which is $ \frac{1}{2}(e^{j2t}+e^{-j2t}) $ according to Euler's Forumla.
Using the property of linearity, the response is: $ t\frac{1}{2}(e^{-j2t}+e^{j2t}) $ which is equal to $ t*cos(2t) $
So if $ x(t) = cos(2t) \rightarrow $ Linear System $ \rightarrow y(t) = tcos(2t) $
