5. Suppose a stationary time series {Xt}t in Z with mean 0 and autocorrelation func tion p(h) = corr(Xt+h, Xt), for h in Z. Show that the best linear predictor of Xn+h of the form aXn is obtained with a =p(h). That is, the function S(a) = E[(Xn+h − aXn)2] is minimised with a =p(h).
[Total 10 marks]