Results 1 to 8 of 8

Math Help - Sum the series

  1. #1
    Junior Member
    Joined
    May 2005
    Posts
    33

    Sum the series

    Sum the series:

    1*2*3-2^3+3*4*5-4^3+...+9999*10000*10001-10000^3.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Junior Member
    Joined
    May 2005
    Posts
    60
    Split the entire series into two parts

    (1*2*3+3*4*5+.........)-(2^3+4^3+.......)

    The first part can be written as Summation[n(n+1)(n+2)]

    Summation (n^3 + 3(n^2) + 2n)
    I hope you can expand for the individual summations.

    For the second part take 2^3 common
    2^3(1+2^3 + 3^3......)
    2^3 Summation(n^3)

    Hope you can take it from here.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    May 2005
    Posts
    33
    - 25,005,000 Correct?
    Each 'group' starts from -2, then add -3+....+-9999+-10000
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Aug 2005
    Posts
    24
    Can someone explain why the summation is like that? I still don't get it.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    May 2005
    Posts
    60
    Can you please explain which part of the summation you didnt understand??
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Newbie
    Joined
    Aug 2005
    Posts
    24
    For the second part take 2^3 common
    2^3(1+2^3 + 3^3......)
    2^3 Summation(n^3)


    This please.
    Then do I add the two summation together? And should I put 5000 for n?
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Junior Member
    Joined
    May 2005
    Posts
    60
    1^3 + 2^3 + 3^3 + 4^3 +........5000^3

    Each number can be written as n^3.

    Since we are adding the numbers we take Summation(n^3)

    Correct n=5000 since we took 2 common.

    There's a negative sign between the two series so techincally you are subtracting one from the other.
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Newbie
    Joined
    Aug 2005
    Posts
    24
    I understand what you are explaining, but how do I calculate or show my working for the whole thing?
    Last edited by ardnas; September 1st 2005 at 09:00 AM.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 5
    Last Post: October 3rd 2011, 02:12 AM
  2. Replies: 3
    Last Post: September 29th 2010, 07:11 AM
  3. Replies: 0
    Last Post: January 26th 2010, 09:06 AM
  4. Replies: 2
    Last Post: December 1st 2009, 01:45 PM
  5. Replies: 1
    Last Post: May 5th 2008, 10:44 PM

Search Tags


/mathhelpforum @mathhelpforum