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Math Help - -2,_____,______,54; geo sequence

  1. #1
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    -2,_____,______,54; geo sequence

    and I don't know how to do this one either:
    1/4,____,4

    Or this one:
    _____,_______,_______,2.5 r=2

    My textbook doesn't go over this either....

    Thanks
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by beetz View Post
    and I don't know how to do this one either:
    1/4,____,4
    recall that the terms of a geometric series are given by:

    a_n = ar^{n - 1} for n = 1,2,3,4...

    where a_n is the nth term, a is the first term, r is the common ratio, and n is the current number of the term.

    here we see that a = \frac 14 and a_3 = ar^2 = \frac 14r^2 = 4

    solve for r and you can find the middle term.

    Or this one:
    _____,_______,_______,2.5 r=2

    My textbook doesn't go over this either....

    Thanks
    here you have a_4 = 2.5 = ar^3 = 8a

    solve for a and you can find the other terms
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