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Homework Help: Geometric series - positive and negative ratio

  1. Apr 1, 2012 #1

    Second term of a geometric series is 48 and the fourth term is 3... Show that one possible value for the common ratio, r, of the series is -1/4 and state the other value.

    ar=48, ar^3= 3... so ar^3/ar=3/48 which simplifies to r^2 = 1/16, therefore r = 1/4

    Can anyone explain where the other solution is from? Or where I am wrong

    Thanks, and sorry if this is in the wrong section, I'm not familiar with pre/post calculus
  2. jcsd
  3. Apr 1, 2012 #2
    Oh, nevermind its because I have rooted the 1/16 meaning it could have been + or - 1/4 to start with. Haha
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