Given the definition of Linear systems
$ \alpha x1(t) + \beta x2(t) <\math> is <math> \alpha y1(t)+ \beta y2(t). $
Consider the following system: $ e^{2jt}\to system\to te^{-2jt} $
$ e^{-2jt}\to system\to te^{2jt} $
From the given system:
$ x(t)\to system\to tx(-t) $
From Euler's formula $ e^{iy}=cos{y}+i sin{y} $
