TeX source:
\begin{array}{lrclcll}& \mathbb{D} &=& \mathbb{R} \\\\& \left(y-3\right)\cdot\left(y^2-\dfrac{2}{3}y-3\right) &=& 0 &\vert & \text{Satz vom Nullprodukt}\\\text{Faktor 1:} & y-3 &=& 0 &\vert & +3 \\& y_1 &=& 3\\\\\text{Faktor 2:} & y^2-\dfrac{2}{3}y-3 &=& 0 &\vert & \text{p-q-Formel} \\& y_{2,3} &=& \dfrac{1}{3}\pm\sqrt{\left(-\dfrac{1}{3}\right)^2+3}\\\\& y_{2,3} &=& \dfrac{1}{3}\pm\sqrt{\dfrac{28}{9}}\\\\& y_2 &=& \dfrac{1+\sqrt{28}}{3} \approx 2{,}10 \\\\& y_3 &=& \dfrac{1-\sqrt{28}}{3} \approx -1{,}43 \\\\& \mathbb{L} &=& \left\{\dfrac{1-2\sqrt{7}}{3}\;;\;\dfrac{1+2\sqrt{7}}{3}\;;\; 3\right\}\end{array}