an = (1/6)(1/2)^(n-1)
Sn = a1+a2+...+an
= (1/3)( 1- (1/2)^n )
1/6+1/12+1/24+...+1/990
=S165
=(1/3)( 1- (1/2)^165 )我是六年级的，看不懂。可以详细吗S =1/6+1/12+1/24+...+1/990(1)
(1/2)*(1) =(2)
(1/2)S =1/12+1/24+1/48+...+1/1980 (2)

(1)-(2)
(1/2)S = 1/6 - 1/1980
S = 2( 1/6 - 1/1980)
= 329/990s什么意思我是六年级的呜呜可以纯数字吗好了马上采纳你设
S =1/6+1/12+1/24+...+1/990可以不要设吗我要过程和结果