Rewrite the model using the backward shift operator b and

Question

For each of the following ARMA(1,1) models:

for which we assume that {W_t}_t is a N(0, σ²) white noise,

1. Rewrite the model using the backward shift operator B and determine the polynomials φ(B) and θ(B).

2. Check if the model is stationary and/or invertible and explain your answers.