will it (mathjax) work?

just enabled using drush.

$ h \leq \frac{1}{2} |\zeta - z| [ |\zeta - z - h| \geq \frac{1}{2} |\zeta - z|] $

implies

$ \left| \frac{1}{\zeta - z - h} - \frac{1}{\zeta - z} \right| = \left| \frac{(\zeta - z) - (\zeta - z - h)}{(\zeta - z - h)(\zeta - z)} \right| \ = \left| \frac{h}{(\zeta - z - h)(\zeta - z)} \right| \ \leq \frac{2 |h|}{|\zeta - z|^2}. $

$ \cos 2\theta = \cos^2 \theta - \sin^2 \theta = 2 \cos^2 \theta - 1.$