更新1:
4/13/27=121/27
F.5 Maths 列式 (數列)
回答 (1)
2009-11-30 12:39 am
✔ 最佳答案
公比 r = 1/3 :首k項的和 : 3 + 1 + 1/3 + ... = 3(1 - (1/3)^k)/(1 - 1/3) = 121/27
1 - (1/3)^k = 242/243
1/243 = (1/3)^k
1/(3^5) = 1/(3^k)
k = 5
等比數列81,27,9,...首k=5項的和
= (81 + 27 + 9 + 3 + 1)
= 27(3 + 1 + 1/3 + 1/9 + 1/27)
= 27 * 121/27
= 121
收錄日期: 2021-04-21 22:08:13
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20091129000051KK01044