SOLUTION: find the sum S8 for the geometric series 6-1.8+0.54-0.162+...

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Question 997593: find the sum S8 for the geometric series 6-1.8+0.54-0.162+...
Answer by Edwin McCravy(20056) About Me  (Show Source):
You can put this solution on YOUR website!
6-1.8+0.54-0.162+...
matrix%281%2C2%2C2nd%2Cterm%29%2Fmatrix%281%2C2%2C1st%2Cterm%29=%28-1.8%29%2F6=-0.3

matrix%281%2C2%2C3rd%2Cterm%29%2Fmatrix%281%2C2%2C2nd%2Cterm%29=0.54%2F%28-1.8%29=-0.3



So there is a common ratio of -0.3.  This is a geometric 
series with r=-0.3 and first term a1=6.

Substitute those with n=8 in the sum formula:

S%5Bn%5D=%28a%5B1%5D%281-r%5En%29%29%2F%281-r%29

S%5B8%5D=%286%281-%28-0.3%29%5E8%29%29%2F%281-%28-0.3%29%29

S%5B8%5D=%286%281-%28-0.3%29%5E8%29%29%2F%281%2B0.3%29

S%5B8%5D=%286%281-%28-0.3%29%5E8%29%29%2F1.3

S%5B8%5D=4.6150818

Edwin