I'm doing a self study out of Box, Jenkins, Reinsal, Ljung - Time Series Analysis Forecasting and Control. Problem 2.2 has me stuck (it seems so simple) it asks:
State whether or not a stationary stochastic process can have the following values of autocorrelations: $$a) \ \rho_1 = .8 \quad \rho_2=0.55\quad \rho_k = 0 \quad k>2$$ $$b) \ \rho_1 = .8 \quad \rho_2 = .28 \quad \rho_k = 0 \quad k>2$$
I'm trying to get some intuition for this. I can't see any reason where there would be restrictions on the autocorrelation function or what values it may take which probably exposes a big hole in my understanding of the chapter. Any advice/intuition/solutions are welcome.