已知等比数列{an}的公比为2,S4=1,求s8
人气：456 ℃ 时间：2020-09-26 20:48:28
解答
S4=a1（1-2^4）/(1-2)=a1(2^4-1)=1
S8=a1(1-2^8)/(1-2)=a1(2^8-1)=a1(2^4-1)(2^4+1)=17
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