TeX source:
\begin{array}{rclcc} f(x) &=& 2x^2-4x+6 & \vert & \text{ausklammern der 2 vor dem } x^2 \cr f(x) &=& 2(x^2-2x+3) \cr f(x) &=& 2(x^2-2x+1+2) \end{array}