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Bin
Bin asked in Science & MathematicsMathematics · 8 years ago

how to findd a sum of geometric series given 2 sums and ratio?

how to find a sum given 2 sums and a ratio... like they gave me s11 and s12.. i need to find s13.. what formula ? please tell me simple steps

3 Answers

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  • Anonymous
    8 years ago
    Favorite Answer

    If you have the ratio (unlike the other question you posted, where no ratio was given), then this is easy.

    The 12th term is T12 = S12 - S11

    The 13 term is just T13 = T12 x r.

    And S13 = S12 + T13

  • Pi R Squared
    Lv 7
    8 years ago

    Hi,

    s12/s11 = r, so s13 = r*s12 = (s12)²/s11 <==ANSWER

    I hope that helps!! :-)

  • Mike G
    Lv 7
    8 years ago

    Sn = a[1-r^n]/[1-r]

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