I have no idea if i am doing this right because i see a whole mess of people having done the same thing. I looked at the problem and saw that
$ \,\ y(t) = tx(-t) $
so for $ \,\ x(t)=cos(2t) $ we will get
$ \,\ y(t) = tcos(-2t) $ which is the same as what everybody else has because $ \,\ cos(-2t) = cos(2t) $
can someone correct me if i am wrong.
