1. if x,y,z form a geometric sequence, where x+y+z=26 and xyz=64, then x+z
2.it is given that the sum of the first n terms of a geometric sequence is sn=1-(-2)^(n)
find the general term of sequence
geometric sequence 20pt
2012-10-02 4:18 pm
回答 (1)
2012-10-02 5:30 pm
✔ 最佳答案
1 Let x = a, y = ar, z = ar^2a(1 + r + r^2) = 26...(1)
(ar)^3 = 64...(2)
From (2): ar = 4
x + z = a + ar^2 = 26 - y = 26 - ar = 22
(2) Consider a_1 = s_1 = 3
s_2 = 1 - (-2)^2 = -3 => a_2 = -6
So, ratio = -1/2 and the general term of sequence is 3(-2)^(n - 1)
收錄日期: 2021-04-27 17:43:25
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20121002000051KK00121