A linear time-invariant system is described by the difference equation
y[n]=x[n]+x[n-4]
(a) Find its impulse response h[n].
(b) Find its system function H(z).
(c) Plot the poles and zeros of H(z) in the z-plane.
(d) Find the frequency response H(e^jw) and express it in polar form (magnitude and phase).
(e) Carefully sketch and label a plot of H(e^jw) for -pi