# User:Tohline/Math/EQ TRApproximation

 $~\Phi_\mathrm{TR}(\varpi,z)$ $~=$ $~-\biggl[ \frac{2GM}{\pi } \biggr]\frac{K(k)}{\sqrt{(\varpi+a)^2 + z^2}}$ $\mathrm{where:}~~~k \equiv \{4\varpi a/[ (\varpi+a)^2 + z^2]\}^{1 / 2}$