TeX source:
\begin{array}{rclcl} \mathbb{D} &=& \mathbb{R} \cr \cr \cr 3x^{2n} &=& 2x^{2n-1}+x^{2n-1} \cr\cr 3x^{2n} &=& 3x^{2n-1} &\vert& : x^{2n-1} \cr\cr \dfrac{3x^{2n}}{x^{2n-1}} &=& \dfrac{3x^{2n-1}}{x^{2n-1}} \cr\cr 3x^{2n-(2n-1)} &=& 3x^{2n-1-(2n-1)} \cr\cr3x^1 &=& 3x^0 \cr 3x &=& 3 &\vert& :3 \cr x &=& 1 \end{array}