About the Project
25 Zeta and Related FunctionsRiemann Zeta Function

§25.4 Reflection Formulas

For s\neq 0,1,

25.4.1 \zeta\left(1-s\right)=2(2\pi)^{-s}\cos\left(\tfrac{1}{2}\pi s\right)\Gamma%
\left(s\right)\zeta\left(s\right),
25.4.2 \zeta\left(s\right)=2(2\pi)^{s-1}\sin\left(\tfrac{1}{2}\pi s\right)\Gamma\left%
(1-s\right)\zeta\left(1-s\right).

Equivalently,

25.4.3 \xi\left(s\right)=\xi\left(1-s\right),

where \xi\left(s\right) is Riemann’s \xi-function, defined by:

25.4.4 \xi\left(s\right)=\tfrac{1}{2}s(s-1)\Gamma\left(\tfrac{1}{2}s\right)\pi^{-s/2}%
\zeta\left(s\right).