8. Answer the following questions and briefly explain your reasoning: a)(i) State clearly what is meant by the PACF in a time series context, commenting in particular on the difference between autocorrelation function (ACF) and partial auto- correlation function (PACF). FINA 304 4 of 6 = (ii) Show that autocorrelation function (ACF) for the AR(1) model y = y-1 + u; is of the form o" for lag n (0