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Homework Help: Geometric progression

  1. Aug 12, 2010 #1
    An infinite geometric progression has a finite sum. Given that the sum of the first two terms is 9 and the third term is 12.

    1/ Find the value of the first term and the common ration r.
  2. jcsd
  3. Aug 12, 2010 #2


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    Work shown?
  4. Aug 13, 2010 #3
    what???? i cannot really understand what you r saying
    i just need help..lolzz...in fact don't really know where to start..y the way i know the equation
  5. Aug 13, 2010 #4


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    Well, I can't just spoonfeed you with the answer.

    A geometric progression can be written as a, ar, ar2, ar3,..., arn

    Where a is the first term, and r is the common ratio

    If the sum of the first two terms is 9, we can rewrite that as

    a + ar = 9

    If the third term is 12, we can rewrite it as

    ar2 = 12

    Now you have 2 equations in 2 unknowns. I think it should be solvable now.
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