Re: [中學] 無窮級數

[mack (腦海裡依然記得妳)]

※ 引述《susiseptem (..)》之銘言：
: 無窮級數 1 至 無窮大 n(1/3)^n 之值
: 感謝板上專業的大大QQ
: 100P答謝
     S = Σn*(1/3)^n     = 1*(1/3)+2*(1/3)^2+3*(1/3)^3+4*(1/3)^4+.....
(1/3)S = Σn*(1/3)^(n+1) =         1*(1/3)^2+2*(1/3)^3+3*(1/3)^4+4*(1/3)^5+...
(2/3)S =                 = 1*(1/3)+  (1/3)^2+  (1/3)^3+  (1/3)^4+.....
                         = (1/3)/[1-(1/3)]
                         = 1/2
     S = 3/4

--
※ 發信站: 批踢踢實業坊(ptt.cc) 
◆ From: 111.252.213.74
推 susiseptem  :謝謝大大 已發給你