Results 1 to 7 of 7

Math Help - Geometric Series challenging question

  1. #1
    Newbie
    Joined
    Jan 2013
    From
    Australia
    Posts
    6

    Exclamation Geometric Series challenging question

    Suppose r and s are positive integers with no common factor and

    1 - 1/2 + 1/3 - 1/4 + ... + 1/1339 - 1/1340 = r/s

    Find a prime factor of r.

    Have no idea how to solve this so please help.

    Please explain it step by step clearly. Thanks.
    Attached Thumbnails Attached Thumbnails Geometric Series challenging question-q5.png   Geometric Series challenging question-q5.png  
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Newbie
    Joined
    Jan 2013
    From
    Australia
    Posts
    6

    Re: Geometric Series challenging question

    So no one knows how to answer this?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,605
    Thanks
    1574
    Awards
    1

    Re: Geometric Series challenging question

    Quote Originally Posted by spriterman View Post
    So no one knows how to answer this?
    Oh no, many of us know what needs to be done.
    But why do you think we should do your work for you?

    Here it is.

    Now what can you do with that?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Jan 2013
    From
    Australia
    Posts
    6

    Re: Geometric Series challenging question

    Doesn't that equation make the 1 negative? The starting term of the series is a positive.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,605
    Thanks
    1574
    Awards
    1

    Re: Geometric Series challenging question

    Quote Originally Posted by spriterman View Post
    Doesn't that equation make the 1 negative? The starting term of the series is a positive.

    Are you saying that you do not know that (-1)^{1-1}=1~?

    If so, no wonder you are having trouble.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Newbie
    Joined
    Jan 2013
    From
    Australia
    Posts
    6

    Re: Geometric Series challenging question

    Quote Originally Posted by Plato View Post
    Are you saying that you do not know that (-1)^{1-1}=1~?

    If so, no wonder you are having trouble.
    Ok sorry, misread the equation.

    But how did you get the equation the first place?
    Last edited by spriterman; January 11th 2013 at 03:30 PM.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,406
    Thanks
    1294

    Re: Geometric Series challenging question

    Also, this is not a geometric series...
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 2
    Last Post: March 21st 2012, 06:52 AM
  2. Geometric Series Question
    Posted in the Algebra Forum
    Replies: 8
    Last Post: December 11th 2011, 07:28 PM
  3. Question about geometric series
    Posted in the Calculus Forum
    Replies: 7
    Last Post: June 1st 2010, 04:07 PM
  4. Another Geometric Series Question.
    Posted in the Algebra Forum
    Replies: 1
    Last Post: April 10th 2009, 01:11 PM
  5. Replies: 1
    Last Post: July 14th 2008, 05:48 AM

Search Tags


/mathhelpforum @mathhelpforum