等比数列求和:1+1/2+1/4+……+1/2^n 等于2-2/2^(n+1) 还是等于2-2/2^n

问题描述:

等比数列求和:1+1/2+1/4+……+1/2^n 等于2-2/2^(n+1) 还是等于2-2/2^n

一共是n+1项
S=1x(1-1/2^(n+1))/(1-1/2)=2-1/2^n