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Thread: Geometric progression

  1. #1
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    Geometric progression

    1)
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    Need to find common ratio(q), also I know that geometric progression is decreasing.

    2)Browser-based, real-time TeX, LaTeX and ASCIIMath visualization...

    Need to find x, I left left side and instead of right side I wrote geometric progresison sum formula but didn't get a result.

    3)
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    Need to find from 5th and 10th(inclusive) terms sum.

    4) 3 numbers, first one is 5, makes arithmetic progression. If we put 9 instead of first number we would get geometric progression. Need to find these 3 arithmetic progression terms.
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  2. #2
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    Re: Geometric progression

    I got second and third one right. I have tried with first one using 4r + 4r^3 = 8(4r^4 + 4r^6) can't get logical result and with fourth I get (5+d)/9=(5+2d)/(5+d) since geometric progression terms are 9, 5+d, 5+2d, is it right or wrong?
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  3. #3
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    Re: Geometric progression

    1) Just divide both sides by 4r(1+r^2). You should find r = 1/2
    2) I don't understand your question
    3) If S10 is the sum of the first 10 terms, then is S10-S4 the answer to your question ?
    4) You have to find d and r such as 5+d=9*r and 5+2d=9*r^2. Then you should be able to find that the numbers are 5,3,1 or 5,15,25.
    Last edited by Hippasus; Sep 29th 2017 at 11:53 PM.
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