# [Calculation 2] Pfaff’s Transformation Formula

Theorem. (Pfaff’s Transformation Formula) $${}_2 F_1(a,b;c;z) = (1-z)^{-a} {}_2 F_1 \left(a,c-b;c; \frac{z}{z-1} \right)$$   Proof. We remember the Euler Integral Representation for the hypergeometric function: $${}_2 F_1 (a,b;c;z) = \frac{\Gamma(c)}{\Gamma(b)\Gamma(c-b)} \int_0^1 t^{b-1}(1-t)^{c-b-1} (1-tz)^{-a}\,dt.$$ Substitution $t=1-s$ yields \begin{eqnarray*} {}_2 … Continue reading