infinite sum

n/4 = 1 - 1/3 + 1/5 - 1/7 + 1/9 - 1/11 + ...

n= 4(1/1 - 1/3 + 1/5 - 1/7 + 1/9 - 1/11 + ... )
= 2(2/1 x 2/3 x 4/3 x 4/5 x 6/5 x 6/7 x 8/7 x 8/9 x ... )
≈ 3.14159 26535 89793 23846 26433 83279 50288...

chun2yau，點解你情願揀阿一果個答咗等於冇答嘅回答都唔願意揀myisland8132果個貼切嘅回答做「最佳解答」？

n=π 證明如下 [要知道1/(1+x^2) 的積分是arctanx]

圖片參考：http://in.geocities.com/myisland8132/7007051000577.gif