For each of the following models (a) xt = 0.3xt1 + zt (b) xt = zt 1.3zt1 + 0.4zt2 (c) xt = 0.5xt1 + zt 1.3zt1 + 0.

For each of the following models

(a) xt = 0.3xt−1 + zt

(b) xt = zt − 1.3zt−1 + 0.4zt−2

(c) xt = 0.5xt−1 + zt − 1.3zt−1 + 0.4zt−2

assume that zt ∼ wn(0, σ2) and express the model in lag polynomial notation, determine whether it isstationary and / or invertible. For model (a), find the MA representation.