TeX source:
\begin{array}{rclcll}\mathbb{D} &=& \mathbb{R} \cr\cr 0 &=& -2\cdot 3^x+9^x-2 \\0 &=& (3^2)^x-2\cdot 3^x-2 \\0 &=& (3^x)^2-2\cdot 3^x-2\end{array}