Consider the following model : Y = Xt + Zt, where {Zt} ~ WN(0, σ^2) and {Xt} is a random process AR(1) with [∅] < 1. This means that {Xt} is stationary such that Xt = ∅ Xt-1 + Et,
where {et} ~ WN(0,σ^2), and E[et+ Xs] = 0) for s < t. We also assume that E[es Zt] = 0 = E[Xs, Zt] for s and all t. (a) Show that the process {Y{} is stationary and calculate its autocovariance function and its autocorrelation function. (b) Consider {Ut} such as Ut = Yt - ∅Yt-1 Prove that yu(h) = 0, if |h| > 1.