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Math Help - 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
    Flow Master
    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) ....

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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) ....

    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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