TeX source:

E[(w_t + \theta_1w_{t-1})(w_{t-h}+\theta_1w_{t-h-1})] = E[w_tw_{t-h} + \theta_1w_{t-1}w_{t-h} +\theta_1w_tw_{t-h-1}+\theta^2_1 w_{t-1}w_{t-h-1}]