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Homework Help: Geometric series problem

  1. Oct 4, 2011 #1
    Geometric series problem urgent

    1. The problem statement, all variables and given/known data

    Calculate the geometric series of Ʃfrom n=1 to infinity of 1/n

    2. Relevant equations



    3. The attempt at a solution
    I dont know how to start solving, how can I solve this? I have test about this tomorrow I really need some help please.
     
  2. jcsd
  3. Oct 4, 2011 #2

    Mark44

    Staff: Mentor

    Re: Geometric series problem urgent

    First off, what is a geometric series? Are you sure that your series is a geometric series?
     
  4. Oct 4, 2011 #3
    Re: Geometric series problem urgent

    the formula is Ʃ from n=0 to ∞ of a(r)^n is equal to a/(1-r)

    I was told to use the geoemtric series and to solve for that. but I dont know any general process or any way to do that. how can I start to solve that?
     
  5. Oct 4, 2011 #4

    Mark44

    Staff: Mentor

    Re: Geometric series problem urgent

    The general term of a geometric series looks like this: ark. Does your series look like this?

    It would be helpful to see the exact wording of your problem. What you have makes almost no sense.
     
  6. Oct 4, 2011 #5
    Re: Geometric series problem urgent

    thats what I have there arent many details i solved some similar problems for instance

    Ʃ from n = 0 to ∞ of 1/2^n by subsituing this in the a/(1-r) expression the result was 2

    but on this problem I dont see how could I make such a substitution.
     
  7. Oct 4, 2011 #6

    SammyS

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    Re: Geometric series problem urgent

    Are you sure that the word 'geometric' is in the problem in your book , wherever you got it.

    This is a well known series that doesn't converge.
     
  8. Oct 4, 2011 #7
    Re: Geometric series problem urgent

    Yes it is there
     
  9. Oct 4, 2011 #8
    Re: Geometric series problem urgent

    Ʃfrom n=1 to infinity of 1/n..this is harmonic series where the n is to the power of 1..
    i just learned this in my class
     
  10. Oct 5, 2011 #9

    SammyS

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    Re: Geometric series problem urgent

    Writing out the first bunch of terms gives:

    1 + 1/2

     + 1/3 + 1/4     This is greater than 1/2, because 1/3 > 1/4

     + 1/5 + 1/6 + 1/7 + 1/8    > 1/2, because each fraction is at least 1/8

     + 9 + 1/10 + 1/11 + 1/12 + 1/13 + 1/14 + 1/15 + 1/16  > 1/2, because each fraction is at least 1/16

     + ...

    If you go far enough, you can exceed any number you like.
     
  11. Oct 5, 2011 #10

    Mark44

    Staff: Mentor

    Re: Geometric series problem urgent

    Moderator's note: Thread moved to Calculus & Beyond section.
     
  12. Oct 5, 2011 #11
    Re: Geometric series problem urgent

    This is a famous series...you will drill this into your head.
     
  13. Oct 5, 2011 #12
    Re: Geometric series problem urgent

    Actually what are you calculating...? The sum? the convergence/divergence? limt?
     
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