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Math Help - Geometric Progression

  1. #1
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    Question Geometric Progression

    Hi

    The first three terms of a geometric progression are 2^n, 2^(n+1),2^(n+2).

    (a) Find n.

    (b) Find the sum of the first 6 terms. Express your answer as a rational number.

    Could someone please show me how to do (a)? I only know the basics of geometric progression (i.e. the formulas) but none of them fit this question somehow.
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  2. #2
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    Quote Originally Posted by xwrathbringerx View Post
    Hi

    The first three terms of a geometric progression are 2^n, 2^(n+1),2^(n+2).

    (a) Find n.

    (b) Find the sum of the first 6 terms. Express your answer as a rational number.

    Could someone please show me how to do (a)? I only know the basics of geometric progression (i.e. the formulas) but none of them fit this question somehow.
    I would hazard a guess that as it stands (a) makes no sense. Try posting the question as it is asked.

    .
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  3. #3
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    typed it word for word from the textbook

    By the way, the answers given by the textbook are:

    (a) n = 1/2

    (b) 93 622.5
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  4. #4
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    Re :

    It is not possible .

    \frac{2^{n+1}}{2^n}=\frac{2^{n+2}}{2^{n+1}} , which simplifies to

    2=2
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  5. #5
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    Quote Originally Posted by mathaddict View Post
    It is not possible .

    \frac{2^{n+1}}{2^n}=\frac{2^{n+2}}{2^{n+1}} , which simplifies to

    2=2
    Which is OK as we have a geometric progression with first term 2^n and common ratio of 2. As it stands there is no way to say anything about n

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