1.The sum of the first 3 terms of a geometric sequence is 63, and the sum of the 4th, 5th and 6th terms id -65/3
Find the common ratio of the sequence.
2.The sum of the first 6 terms of a geometric sequence is 28 times the sum of the
first 3 terms.
Find the common ratio of the sequence
geometric sequence 20pt
2012-10-02 4:15 pm
回答 (1)
2012-10-02 6:31 pm
✔ 最佳答案
Let the first term is a and the common ratio is r1 The value should be -56/3
a(1 + r + r^2) = 63
ar^3(1 + r + r^2) = -56/3
So, 63r^3 = -56/3
r^3 = -8/27
r = -2/3
The common ratio of the sequence is -2/3
2 a(1 + r + r^2) + ar^3(1 + r + r^2) = 28a(1 + r + r^2)
ar^3(1 + r + r^2) = 27a(1 + r + r^2)
r^3 = 27
r = 3
The common ratio of the sequence is 3
收錄日期: 2021-04-27 17:45:20
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