Functional equation for Riemann zeta with cosine

Theorem

The following formula holds for all $z \in \mathbb{C}$: $$\zeta(1-z)=2^{1-z} \pi^{-z} \cos \left( \dfrac{\pi z}{2} \right)\Gamma(z)\zeta(z),$$ where $\zeta$ denotes Riemann zeta, $\pi$ denotes pi, $\cos$ denotes cosine, and $\Gamma$ denotes gamma.

References

• 1930: {{ #if: |{{{2}}}|Edward Charles Titchmarsh}}{{#if: |{{#if: |, [[Mathematician:{{{author2}}}|{{ #if: |{{{2}}}|{{{author2}}}}}]]{{#if: |, [[Mathematician:{{{author3}}}|{{ #if: |{{{2}}}|{{{author3}}}}}]]{{#if: |, [[Mathematician:{{{author4}}}|{{ #if: |{{{2}}}|{{{author4}}}}}]]{{#if: |, [[Mathematician:{{{author5}}}|{{ #if: |{{{2}}}|{{{author5}}}}}]] and [[Mathematician:{{{author6}}}|{{ #if: |{{{2}}}|{{{author6}}}}}]]| and [[Mathematician:{{{author5}}}|{{ #if: |{{{2}}}|{{{author5}}}}}]]}}| and [[Mathematician:{{{author4}}}|{{ #if: |{{{2}}}|{{{author4}}}}}]]}}| and [[Mathematician:{{{author3}}}|{{ #if: |{{{2}}}|{{{author3}}}}}]]}}| and [[Mathematician:{{{author2}}}|{{ #if: |{{{2}}}|{{{author2}}}}}]]}}|}}: [[Book:Edward Charles Titchmarsh/The Zeta-Function of Riemann{{#if: |/Volume {{{volume}}}|}}{{#if: |/{{{edpage}}}}}|The Zeta-Function of Riemann{{#if: |: Volume {{{volume}}}|}}{{#if: |: {{{eddisplay}}}|{{#if: | ({{{ed}}} ed.)}}}}]]{{#if: | (translated by [[Mathematician:{{{translated}}}|{{ #if: |{{{2}}}|{{{translated}}}}}]])}}{{#if: |, {{{publisher}}}|}}{{#if: |, ISBN {{{isbn}}}|}}{{#if: Functional equation for Riemann zeta | ... (previous)|}}{{#if: Riemann xi | ... (next)|}}{{#if: |: Entry: {{#if: |[[{{{entryref}}}|{{{entry}}}]]|{{{entry}}}}}|}}: § Introduction $(6')$