mitosuki
What is the sum of an 8–term geometric series if the first term is –11, the last term is 859,375, and the common ratio is –5?
–143,231
716,144
144,177
–36,047
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mitosuki
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716,144?
Tomas.A
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I got -716144
Tomas.A
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what formula you used? \[S=a\frac{1-r^n}{1-r}\]
this?
mitosuki
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No it looks like:
a1 - a1 (r)^n
Sn = _______________
1 - r
Tomas.A
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it's same
Tomas.A
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a1-a1r^n=a1(1-r^n)
Tomas.A
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i calculated wrongly, you are correct, sorry
mitosuki
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Haha it's ok, thank you
Tomas.A
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i calculated as
\[S=a\frac{r^n-1}{1-r}\]
mixed r^n and 1 ><
malice
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Ty!!! This was correct!