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Math Help - Geometric sequences

  1. #1
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    Geometric sequences

    In a given geometric sequence gn, g4 = 5 and g6 = 11.25. What is g14/g17?

    The answer is 8/27. The book uses the geometric sequence formula... I don't understand why they plug certain numbers in. For example... The formula is an=a1r^(n-1)

    How do you know what to put in for a1? The book puts in g4 as "a1."
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    Re: Geometric sequences

    Quote Originally Posted by benny92000 View Post
    In a given geometric sequence gn, g4 = 5 and g6 = 11.25. What is g14/g17?

    The answer is 8/27. The book uses the geometric sequence formula... I don't understand why they plug certain numbers in. For example... The formula is an=a1r^(n-1)

    How do you know what to put in for a1? The book puts in g4 as "a1."
    Yes, to simplify things let g4 be the first term so that a1 = 5. Then g6 is the third term. Then 11.25 = 5(r^2) and you then solve for r etc.

    an=a1r^(n-1) is the usual general term of a geometric sequence.
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