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Thread: Finite geometric Series Problem

  1. #1
    anthonycronin
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    Finite geometric Series Problem

    Hello i wondering if anyone could give me a hand solving this

    Given
    1. the sum of the geometric progression := S
    2. the number of terms := n
    3. the first term := t

    Can you get an equation for the common ratio???

    finite G.P S = t * ( 1 - r^n)/(1 - r)


    the number i workin off are
    S = 292.618
    n = 15
    t = 50

    i dont know the sequence as i'm using this for a c++ program and numbers vary!
    Anto!!!
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by anthonycronin View Post
    Hello i wondering if anyone could give me a hand solving this

    Given
    1. the sum of the geometric progression := S
    2. the number of terms := n
    3. the first term := t

    Can you get an equation for the common ratio???

    finite G.P S = t * ( 1 - r^n)/(1 - r)


    the number i workin off are
    S = 292.618
    n = 15
    t = 50

    i dont know the sequence as i'm using this for a c++ program and numbers vary!
    Anto!!!
    In the spirit of the challenge of finding the oldest unanswered post, this question is after a bit of jiggery pokery asking for solutions of:

    r^n-\frac{S}{t}r+\frac{S-t}{t}=0

    or rewritting this:

    Can we find one or more real roots of:

    r^n-ar+b=0

    in closed form when n>4.


    (The condition on n is because we have the formulas for the roots for n=1,\ 2,\ 3,\ 4. Though something more elegant for the last two cases would be nice).

    CB
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  3. #3
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    mr fantastic's Avatar
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    Quote Originally Posted by CaptainBlack View Post
    In the spirit of the challenge of finding the oldest unanswered post, this question is after a bit of jiggery pokery asking for solutions of:

    r^n-\frac{S}{t}r+\frac{S-t}{t}=0

    or rewritting this:

    Can we find one or more real roots of:

    r^n-ar+b=0

    in closed form when n>4.


    (The condition on n is because we have the formulas for the roots for n=1,\ 2,\ 3,\ 4. Though something more elegant for the last two cases would be nice).

    CB
    I thought unanswered posts that old got deleted during the 'Great Purge' (it obviously wasn't in Urgent Help forum) ....

    http://www.youtube.com/watch?v=grbSQ6O6kbs
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  4. #4
    Grand Panjandrum
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    Quote Originally Posted by mr fantastic View Post
    I thought unanswered posts that old got deleted during the 'Great Purge' (it obviously wasn't in Urgent Help forum) ....

    YouTube - Monty Python-Bring out your dead!
    Of all places to find it it was in Number Theory !?

    (When I was younger I was at the recording of at least one episode Monty Python).

    CB
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