1. The problem statement, all variables and given/known data Consider the AR(2) model (1 - x1*B - x2*B^2)Xt = εt. Show that Xt is a stationary process if and only if the following inequalities are satisfied: x1+ x2 < 1 x2-x1< 1 |x2| < 1 3. The attempt at a solution 1 - x1*B - x2*B^2 = 0 |B| > 1 so then use quadratic formula to get B = (-x1 +- sqrt(x1^2 + 4x2)) / (2x2) Do I need to consider all 6 cases (x2 > 0, x2=0, x2 < 0, x1 > 0, x1=0, x1<0)? I think at some point I have to mess with complex roots. Is there an easier way of looking at this problem or do I have to go through each case?