The equation of the system is
y(t)= t * x(-t)
the example in the problem tells us that $ e^2jt $ = t * $ e^-2jt $
and
$ e^-2jt $ = t * $ e^2jt $
Therefore, for x(t)=cos(2t)
we have,
y(t)= t cos(-2t)
= t cos(2t) ( as we know that cos(-t)= cos (t))
