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【趣味數(shù)學(xué)題】ζ-函數(shù)無窮級數(shù)

2021-12-31 03:36 作者:AoiSTZ23  | 我要投稿

鄭濤(Tao Steven Zheng)著

【問題】

以下三道題是我創(chuàng)造的涉及ζ-函數(shù)(Zeta function)的無窮級數(shù)問題。

注:(1)ζ-函數(shù)的無窮級數(shù)(infinite series)表達(dá)式是 %5Czeta%20(x)%20%3D%20%5Csum_%7Bn%3D1%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7Bn%5Ex%7D;(2)ζ-函數(shù)又稱 “黎曼ζ-函數(shù)”(Riemann Zeta function)。

題一: 證明 %5Czeta%20(x)%20%3D%20%5Cfrac%7B2%5Ex%7D%7B2%5Ex%20-%201%7D%20%5Csum_%7Bn%3D0%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7B%7B(2n%2B1)%7D%5E%7Bx%7D%7D。

題二:已知 %20%5Czeta%20(2)%20%3D%20%5Cfrac%7B%7B%5Cpi%7D%5E%7B2%7D%7D%7B6%7D, 推算 A%20%3D%20%5Csum_%7Bn%3D0%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7B%7B(2n%2B1)%7D%5E%7B2%7D%7DB%20%3D%20%5Csum_%7Bn%3D0%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7B%7B(2n%2B2)%7D%5E%7B2%7D%7D

題三: 推算 %20%5Csum_%7Bn%3D1%7D%5E%7B%5Cinfty%7D%20%7B%5Cleft(%5Cfrac%7B1%7D%7Bn(n%2B1)%7D%20%5Cright)%7D%5E%7B2%7D。

【題解】

題一

%5Czeta%20(x)%20%3D%20%5Csum_%7Bn%3D1%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7Bn%5Ex%7D%20%3D%201%20%2B%20%5Cfrac%7B1%7D%7B2%5Ex%7D%20%2B%20%5Cfrac%7B1%7D%7B3%5Ex%7D%20%2B%20%5Cfrac%7B1%7D%7B4%5Ex%7D%20%2B%20%5Cfrac%7B1%7D%7B5%5Ex%7D%20%2B%20...

%5Czeta%20(x)%20%3D%201%20%2B%20%5Cleft(%5Cfrac%7B1%7D%7B2%5Ex%7D%20%2B%20%5Cfrac%7B1%7D%7B4%5Ex%7D%20%2B%20%5Cfrac%7B1%7D%7B8%5Ex%7D%20%2B%20%5Cfrac%7B1%7D%7B16%5Ex%7D%20%2B%20...%20%5Cright)%20%2B%20%5Cleft(%5Cfrac%7B1%7D%7B3%5Ex%7D%20%2B%20%5Cfrac%7B1%7D%7B6%5Ex%7D%20%2B%20%5Cfrac%7B1%7D%7B12%5Ex%7D%20%2B%20%5Cfrac%7B1%7D%7B24%5Ex%7D%20%2B%20...%20%5Cright)%20%2B%20%5Cleft(%5Cfrac%7B1%7D%7B5%5Ex%7D%20%2B%20%5Cfrac%7B1%7D%7B10%5Ex%7D%20%2B%20%5Cfrac%7B1%7D%7B20%5Ex%7D%20%2B%20%5Cfrac%7B1%7D%7B40%5Ex%7D%20%2B%20...%20%5Cright)%20%2B%20...%20

%5Czeta%20(x)%20%3D%201%20%2B%20%5Cfrac%7B1%7D%7B2%5Ex%20-%201%7D%20%2B%20%5Cfrac%7B2%5Ex%7D%7B2%5Ex%20-%201%7D%20%5Csum_%7Bn%3D0%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7B%7B(2n%2B1)%7D%5E%7Bx%7D%7D

%5Czeta%20(x)%20%3D%20%5Cfrac%7B2%5Ex%7D%7B2%5Ex%20-%201%7D%20%2B%20%5Cfrac%7B2%5Ex%7D%7B2%5Ex%20-%201%7D%20%5Csum_%7Bn%3D1%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7B%7B(2n%2B1)%7D%5E%7Bx%7D%7D%20

%5Czeta%20(x)%20%3D%20%5Cfrac%7B2%5Ex%7D%7B2%5Ex%20-%201%7D%20%5Csum_%7Bn%3D0%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7B%7B(2n%2B1)%7D%5E%7Bx%7D%7D


題二
(1)推算 A%20%3D%20%5Csum_%7Bn%3D0%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7B%7B(2n%2B1)%7D%5E%7B2%7D%7D。

從題一的結(jié)果得

%5Czeta%20(2)%20%3D%20%5Cfrac%7B2%5E2%7D%7B2%5E2%20-%201%7D%20%5Csum_%7Bn%3D0%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7B%7B(2n%2B1)%7D%5E%7B2%7D%7D%20

%5Czeta%20(2)%20%3D%20%5Cfrac%7B4%7D%7B3%7D%20%5Csum_%7Bn%3D0%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7B%7B(2n%2B1)%7D%5E%7B2%7D%7D%20

已知 %20%5Czeta%20(2)%20%3D%20%5Cfrac%7B%7B%5Cpi%7D%5E%7B2%7D%7D%7B6%7D%20,那么

%5Csum_%7Bn%3D0%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7B%7B(2n%2B1)%7D%5E%7B2%7D%7D%20%3D%20%5Cfrac%7B3%7D%7B4%7D%5Ctimes%20%5Cfrac%7B%7B%5Cpi%7D%5E%7B2%7D%7D%7B6%7D%20

%5Csum_%7Bn%3D0%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7B%7B(2n%2B1)%7D%5E%7B2%7D%7D%20%3D%20%5Cfrac%7B%7B%5Cpi%7D%5E%7B2%7D%7D%7B8%7D


(2)推算 B%20%3D%20%5Csum_%7Bn%3D0%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7B%7B(2n%2B2)%7D%5E%7B2%7D%7D。

因?yàn)?A%20%2B%20B%20%3D%20%5Cfrac%7B%7B%5Cpi%7D%5E%7B2%7D%7D%7B6%7D%20,

%5Csum_%7Bn%3D0%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7B%7B(2n%2B2)%7D%5E%7B2%7D%7D%20%2B%20%5Cfrac%7B%7B%5Cpi%7D%5E%7B2%7D%7D%7B8%7D%20%3D%20%5Cfrac%7B%7B%5Cpi%7D%5E%7B2%7D%7D%7B6%7D%20

因此,

%20%5Csum_%7Bn%3D0%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7B%7B(2n%2B2)%7D%5E%7B2%7D%7D%20%3D%20%5Cfrac%7B%7B%5Cpi%7D%5E%7B2%7D%7D%7B24%7D

從這個解法得知 A%20%3D%203B。


題三


%20%5Csum_%7Bn%3D1%7D%5E%7B%5Cinfty%7D%20%7B%5Cleft(%5Cfrac%7B1%7D%7Bn(n%2B1)%7D%20%5Cright)%7D%5E%7B2%7D%20%3D%20%5Csum_%7Bn%3D1%7D%5E%7B%5Cinfty%7D%20%7B%5Cleft(%5Cfrac%7B1%7D%7Bn%7D%20-%5Cfrac%7B1%7D%7Bn%2B1%7D%20%5Cright)%7D%5E%7B2%7D

%20%5Csum_%7Bn%3D1%7D%5E%7B%5Cinfty%7D%20%7B%5Cleft(%5Cfrac%7B1%7D%7Bn%7D%20-%5Cfrac%7B1%7D%7Bn%2B1%7D%20%5Cright)%7D%5E%7B2%7D%20%3D%20%5Csum_%7Bn%3D1%7D%5E%7B%5Cinfty%7D%20%5Cleft(%5Cfrac%7B1%7D%7Bn%5E2%7D%20-%5Cfrac%7B2%7D%7Bn(n%2B1)%7D%2B%5Cfrac%7B1%7D%7B%7B(n%2B1)%7D%5E%7B2%7D%7D%20%5Cright)%20%20

已知:

%5Csum_%7Bn%3D1%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7Bn%5E2%7D%20%3D%20%5Czeta(2)%20%3D%20%5Cfrac%7B%7B%5Cpi%7D%5E%7B2%7D%7D%7B6%7D

%5Csum_%7Bn%3D1%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7B%7B(n%2B1)%7D%5E%7B2%7D%7D%20%3D%20%5Czeta(2)%20-1%20%3D%20%5Cfrac%7B%7B%5Cpi%7D%5E%7B2%7D%7D%7B6%7D%20-%201%20

%5Csum_%7Bn%3D1%7D%5E%7B%5Cinfty%7D%20%5Cfrac%7B1%7D%7Bn(n%2B1)%7D%20%3D%20%5Csum_%7Bn%3D1%7D%5E%7B%5Cinfty%7D%20%5Cleft(%5Cfrac%7B1%7D%7Bn%7D%20-%20%5Cfrac%7B1%7D%7Bn%2B1%7D%5Cright)%20%3D%201


所以,

%5Csum_%7Bn%3D1%7D%5E%7B%5Cinfty%7D%20%7B%5Cleft(%5Cfrac%7B1%7D%7Bn(n%2B1)%7D%20%5Cright)%7D%5E%7B2%7D%20%3D%202%5Ctimes%20%5Czeta(2)%20-%201%20-%202%5Ctimes%201%20

%5Csum_%7Bn%3D1%7D%5E%7B%5Cinfty%7D%20%7B%5Cleft(%5Cfrac%7B1%7D%7Bn(n%2B1)%7D%20%5Cright)%7D%5E%7B2%7D%20%3D%202%5Ctimes%20%5Cfrac%7B%7B%5Cpi%7D%5E%7B2%7D%7D%7B6%7D%20-%203%20

%5Csum_%7Bn%3D1%7D%5E%7B%5Cinfty%7D%20%7B%5Cleft(%5Cfrac%7B1%7D%7Bn(n%2B1)%7D%20%5Cright)%7D%5E%7B2%7D%20%3D%20%5Cfrac%7B%7B%5Cpi%7D%5E%7B2%7D%7D%7B3%7D%20-%203


關(guān)鍵詞:ζ-函數(shù)、無窮級數(shù)、黎曼




【趣味數(shù)學(xué)題】ζ-函數(shù)無窮級數(shù)的評論 (共 條)

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