數學sum to infinity of GS

2011-11-19 10:44 pm

The sum to infinity of the geometric sequence 8+6+4+2+2+2/3+... is

A:24
B:25
C:26
D:27

回答 (3)

2011-11-20 2:29 am

✔ 最佳答案

8 + 6 + 4 + 2 + 2 + 2/3 +...

= (8 + 4 + 2 + ... ) + (6 + 2 + 3/2 + ...)

= 8/(1 - 1/2) + 6/(1 - 1/3)

= 16 + 9

= 25

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2011-11-20 1:10 am

There are indeed 2 series, (8 + 4 + 2 + ...) and (6 + 2 + 2/3 +...)
The sum is 25

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2011-11-20 12:22 am

8, 6, 4, 2, 2, 2/3 is NOT a geometric sequence.

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