SOLUTION: Find S17 for the series 8 - 4 + 2 - 1+ ...

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Question 1202481: Find S17 for the series 8 - 4 + 2 - 1+ ...
Found 2 solutions by mananth, ikleyn:
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
just solved
check todays solutions

Answer by ikleyn(52787) About Me  (Show Source):
You can put this solution on YOUR website!
.


        The formula and the final answer/value in the post by @mananth (to which he refers) are incorrect.
        I came to bring a correct solution/answer. 


S%5Bn%5D = a%2A%28%281-r%5En%29%2F%281-r%29%29


a = 8

r = -1/2

S%5B17%5D = 8%2A%281-%28-0.5%29%5E17%29%29%2F%281-%28-0.5%29%29

S%5B17%5D = 5.3333740234375  (exact value).

Solved (correctly).