(a)  Show that the three LTI systems with impulse response

                                             h₁(t)= u (t)

                                             h₂(t)= -2 δ (t) +5 e^-2t u (t)

And

                                     h₃ (t) = 2te^-tu (t)

All have same responses to     

 x (t) = cos (t).

  (b)   Find the impulse responses of another LTI system with the same response to cos (t). This problem illustrate the fact that the response to cos (t) cannot be used to specify an LTI system uniquely.