1. For each of the models (1)-(3), write corresponding characteristic polynomials @(2) and o(z). In other words, write models (1)-(3) as o(B)X, = 0(B)Z, and specify polynomials @(=) and o(z). For each, identify the model as a certain (S)ARIMA model and determine whether the model in invertible and stationary: (1) X4 = -0.2Xt-1+2-274-1; (2) Xt = Xt-1+2-0.2Z-1-0.7Zt-2; (3) Xt-Xt-3 = Z:+0.42-1-0.45Z-2