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3 Let A(z) and B(z) denote the Z transforms of two sequences a,,, N1 Z. Prove that the product C(z) = A(z)B(z) can be written as Na+Ms E ckz_k k=N1+M; where the coefficients are given by the discrete convolution Ck = E agmbm E bk m with appropriate limits for the summation index m. Now consider the func- tions s 1+ 271\\ )= 3 st B =vE () k=6 with the coefficients , 6