1. The problem statement, all variables and given/known data x[n] = anu[n] A discrete system y[n] = −1/2y[n − 1] + x[n]; where x[n] and y[n] in- and output of the system, respectively. Find the system transfer function H(z), and sketch its zeros and poles in the z-plane 2. Relevant equations u[n] is the unit step function 3. The attempt at a solution I transformed x[n] to X(z) but what confuses is the-1/2y[n-1], which basically means the previous -half of the previous output plus the input is equal to out put. but I don't know how to represent the previous output.