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mitosuki

  • 3 years ago

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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  1. mitosuki
    • 3 years ago
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    716,144?

  2. Tomas.A
    • 3 years ago
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    I got -716144

  3. Tomas.A
    • 3 years ago
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    what formula you used? \[S=a\frac{1-r^n}{1-r}\] this?

  4. mitosuki
    • 3 years ago
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    No it looks like: a1 - a1 (r)^n Sn = _______________ 1 - r

  5. Tomas.A
    • 3 years ago
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    it's same

  6. Tomas.A
    • 3 years ago
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    a1-a1r^n=a1(1-r^n)

  7. Tomas.A
    • 3 years ago
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    i calculated wrongly, you are correct, sorry

  8. mitosuki
    • 3 years ago
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    Haha it's ok, thank you

  9. Tomas.A
    • 3 years ago
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    i calculated as \[S=a\frac{r^n-1}{1-r}\] mixed r^n and 1 ><

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