TeX Quellcode:

\begin{array}{rclcl} \dfrac{21}{x^3-7x}-4x &=& \dfrac{6}{x^3-7x} &\vert & \cdot \left(x^3-7x\right) \cr 21-4x(x^3-7x) &=& 6 &\vert & -6 \cr -4x^4+28x^2+15 &=& 0 \cr -4\left(x^2\right)^2+28x^2+15 &=& 0 \end{array}