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Math Help - geometric progression?

  1. #1
    Senior Member sfspitfire23's Avatar
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    geometric progression?

    Given a series a1, a2, a3, . an. If a1 = 25 and every term in the series is -2 times its previous number, then which column is larger?
    Col A: a100
    Col B: -10,000

    Is this a geometric progression? So, we would use the formula an=ar^(n-1)=25(-2)^-99. This is much less than -10,000. So B is larger.
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  2. #2
    MHF Contributor Also sprach Zarathustra's Avatar
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    why 25(-2)^-99?

    why for the minus before 99?
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  3. #3
    Senior Member sfspitfire23's Avatar
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    err sorry....its 25(-2)^99
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  4. #4
    MHF Contributor Also sprach Zarathustra's Avatar
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    2^10=1024

    so 2^99=very huge number...
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  5. #5
    MHF Contributor chiph588@'s Avatar
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    Quote Originally Posted by Also sprach Zarathustra View Post
    2^10=1024

    so 2^99=very huge number...
     \displaystyle{25\cdot2^{99}>10000\implies 25\cdot(-2)^{99}<-10000}
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