A periodic "square wave" sequence is given by π(n) = mNnmN+L-1 ; m = 0, 1, 2,... mN+L≤ n ≤ (m + 1) N − 1 where N is the fundamental period and L/N is the duty cycle. a. Determine an expression for |Ñ(k)| in terms of L and N. b. Plot the magnitude |X (k) for L = 5, N = 20; L = 5, N = 40; L = 5, N = 60; and L = 7, N = 60. c. Comment on the results.