TeX source:
\begin{array}{rcl}\mathbb{D} &=& \mathbb{R} \cr\cr f(x) &=& \dfrac{2}{7}x^{14} \cr \cr \cr f'(x) &=& \dfrac{2}{7} \cdot 14 \cdot x^{14-1} \cr\cr &=& 4x^{13} \end{array}