For the AR(2) series shown below, first check whether they are causal or not. Then use find the ACF (h) for h=0,1,2,,4 following slide 35 from the lecture notes for Week 2 and plot the ACF values to lag 4 (You can use ARMAacf in R as a check on your answers) a xt+1.6xt1+0.64xt2=wt b xt0.40xt10.45xt2=wt