Answer:
AR(2) model is not stationary
Explanation:
Given model  :  Yt = 0.803yt-1  +  0.682yt-2 +  ut  ---- ( 1 )
ut = noise error process
Aim : Check estimated model for stationarity
step 1 : represent the estimated polynomial of the model ( where: ut ∪ N(o,б^2 ) rewrite equation 1
Yt - 0.803yt-1  - 0.682yt-2  = ut  ------- ( 2 )
hence the polynomial can be represented as :
( 1 - 0.803B - 0.682B^2 )Yt = ut
Characteristic of the obtained polynomial can be represented as ;
1 - 0.803λ - 0.682λ^2 - 1 = 0
attached below is the remaining part of the solution