Fairly Impossible#1

Calculus Level 3

1 π n = 1 Γ ( n 1 / 2 ) Γ ( 1 / 2 + 1 ) Γ ( n + 1 ) \frac1\pi \sum_{n=1}^{\infty}\frac{\Gamma(n-1/2)\Gamma(1/2+1)}{\Gamma(n+1)} Evaluate the expression above.


The answer is 1.

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1 solution

Aruna Yumlembam
Jun 21, 2020

Using the fact that, n = 1 Γ ( x + n 1 ) Γ ( y + 1 ) Γ ( n + x + y ) \sum_{n=1}^{\infty}\frac{\Gamma(x+n-1)\Gamma(y+1)}{\Gamma(n+x+y)} = = Γ ( x ) Γ ( y ) Γ ( x + y ) \frac{\Gamma(x)\Gamma(y)}{\Gamma(x+y)} .Then simply letting y = 1 / 2 y=1/2 and x = 1 / 2 x=1/2 ,we have our sum with the result as π \pi ,since Γ ( 1 / 2 ) \Gamma(1/2) = = π \sqrt\pi .Then,

π π \frac{\pi}{\pi} = = 1 1 ,for the proof of this result look at the discussion on the iterated properties of Beta Function.

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