TeX source:
\begin{array}{lclcrcl}\quad\mathbb{D}&=&\mathbb{R}\cr \cr f(z) &=& \dfrac{23}{z^{-42}}\cr \cr &=& 23z^{42}\cr \cr\cr f'(z) &=& 42 \cdot 23z^{41}\cr \cr &=& 966z^{41}\end{array}