Consider a discreet time series / stochastic process -

where is white noise i.e. iid ~

I need to to prove this series is weak stationary when

Definition of weak stationary, I have/use

1. = constant, (independent of t)

2. i.e. independent of t, it is just a function of lag period, k.

I know this is a pretty basic question, but not really able to go ahead here. Can anyone please help with pointers, references, outline of the proof. Thanks