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A linear time-invariant system is described by the difference equation y[n]=x[n]+x[n4] (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. (Recall that 1=ejk where k is an odd integer.) (d) Find the frequency response H(ej) and express it in polar form (magnitude and phase). (e) Carefullv sketch and label a plot of H(ej) for