SOLUTION: find the sum of the first nine terms of the geometric sequence: 8,-16,32,-64,128,...

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Question 972330: find the sum of the first nine terms of the geometric sequence: 8,-16,32,-64,128,...
Answer by josgarithmetic(39618) About Me  (Show Source):
You can put this solution on YOUR website!
common ration -2, first term, 8.

You can look for the formula in a textbook or a reference manual:


The sum of the first n terms of geometric sequence, common ratio r, first term A%5B1%5D is:
A%5B1%5D%28%281-r%5En%29%2F%281-r%29%29

Your series,
8%28%281-%28-2%29%5E9%29%2F%281-%28-2%29%29%29------simplify.