TeX source:

\begin{eqnarray} \text{Var}(x_t) &=& \text{Var}(\delta)+\text{Var}(\phi_1 x_{t-1})+\text{Var}(w_t)       \nonumber \\   &=& \phi_1^2 \text{Var}(x_{t-1})+\sigma^2_w\end{eqnarray}