![{\displaystyle {\displaystyle
\sum_{n=0}^\infty\frac{\lambda+n}\lambda \frac{n!}{\pochhammer{2\lambda}{n}} r^n \Ultra{\lambda}{n}@{x} \Ultra{\lambda}{n}@{y}
=\frac{1-r^2}{(1-2rxy+r^2)^{\lambda+1}}
\HyperpFq{2}{1}@@{\frac12(\lambda+1),\frac12(\lambda+2)}{\lambda+\frac12}{\frac{4r^2(1-x^2)(1-y^2)}{(1-2rxy+r^2)^2}}
(r\in(-1,1),\;x,y\in[-1,1])
}}](/index.php?title=Special:MathShowImage&hash=ac6f07ddcad881f300249ca698249e92&mode=latexml)
Proof
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Symbols List
: sum : http://drmf.wmflabs.org/wiki/Definition:sum
: Pochhammer symbol : http://dlmf.nist.gov/5.2#iii
: ultraspherical/Gegenbauer polynomial : http://dlmf.nist.gov/18.3#T1.t1.r5
: generalized hypergeometric function : http://dlmf.nist.gov/16.2#E1
: element of : http://dlmf.nist.gov/front/introduction#Sx4.p1.t1.r9
Bibliography
Equation in Section 9.8 of KLS.
URL links
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