Consider the following ARMA(2,1) process, where et is Gaussian white noise:

Tt=1.37t-1- 0.4t-2 +t + 0.6 6-1,

E NO, 0.2).

(a) Show that one of the two roots of the characteristic polynomial is 2 and find the other. Is he process stationary? Justify. (b) Find the values 1 and a/a of the MA(co) expansion of the process:

Tt=t t V1t-1 t V26t-2 t V3t-3 t

(c) Give the system of equations that allows to determine the autocovariance coefficients 0 1 and v2 of the process and explain how to obtain the coefficients u for l = 3, 4,.. as a function of the coefficients k, k = 1,...,l-1.