anonymous
  • anonymous
Find the sum of the geometric sequence –3, 15, –75, 375, … when there are 8 terms and select the correct answer below.
Algebra
  • Stacey Warren - Expert brainly.com
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SOLVED
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chestercat
  • chestercat
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anonymous
  • anonymous
what is r?
anonymous
  • anonymous
What is what?
anonymous
  • anonymous
the common ratio

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More answers

anonymous
  • anonymous
Is it 5?
anonymous
  • anonymous
Or -5?
anonymous
  • anonymous
-5 looks right
SolomonZelman
  • SolomonZelman
\(\large\color{black}{ \displaystyle {\rm S}_{\rm n}=\frac{a_1\times \left(1-{\rm r}^{\rm n}\right)}{1-{\rm r}} }\) this is the formula, for the sum of a geometric sequence that starts from some \(a_1\) and has n terms.
SolomonZelman
  • SolomonZelman
you need to find r, identify the \(a_1\) that you are given, and tell me the number of terms (which you plug in for n). plug everything into the formula, and calculate.
anonymous
  • anonymous
I think I did something wrong in the equation because I got 24,414,063
SolomonZelman
  • SolomonZelman
holly molly.....
SolomonZelman
  • SolomonZelman
yeah it is wrong
SolomonZelman
  • SolomonZelman
tell me what was your common ratio (r)? what was your number of terms? what is the first term?
anonymous
  • anonymous
My common ratio was -5 The number of terms was 8 The first term was -3
SolomonZelman
  • SolomonZelman
yes
anonymous
  • anonymous
\((1-(r^n))\) is what I meant
SolomonZelman
  • SolomonZelman
\(\large\color{black}{ \displaystyle {\rm S}_8=\frac{ (-3)\times \left(1-(-5)^8\right)}{1-(-5)} }\) Click \(\bf\color{blue }{\href{http:///www.wolframalpha.com/input/?i=%28-3+%C3%97+%281+-+%28-5%29%5E8%29%29%2F%281-%28-5%29%29}{here}}\) to check the result.
anonymous
  • anonymous
My common ratio was -5 The number of terms was 8 The first term was -3
anonymous
  • anonymous
Is the answer 195,312??
SolomonZelman
  • SolomonZelman
yes, that is the answer.
anonymous
  • anonymous
Thank you so much!
SolomonZelman
  • SolomonZelman
anytime !

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