Results 1 to 3 of 3

Math Help - double summation

  1. #1
    Junior Member
    Joined
    Sep 2008
    Posts
    33
    Thanks
    1

    double summation

    (sorry i dont know how to do the summation symbol)

    double summation, j=1 to 4 and k=2 to 8 (j*k)

    is there a specific formula you are supposed to use?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Moo
    Moo is offline
    A Cute Angle Moo's Avatar
    Joined
    Mar 2008
    From
    P(I'm here)=1/3, P(I'm there)=t+1/3
    Posts
    5,618
    Thanks
    6
    Hello,
    Quote Originally Posted by jlt1209 View Post
    (sorry i dont know how to do the summation symbol)

    double summation, j=1 to 4 and k=2 to 8 (j*k)

    is there a specific formula you are supposed to use?
    \sum_{j=1}^4 \sum_{k=2}^8 jk=\sum_{j=1}^4 \left( \sum_{k=2}^8 jk\right)
    In the second summation, since j doesn't depend on k, you can get it out from the sum :
    =\sum_{j=1}^4 \left(k \sum_{j=1}^8 j\right)

    You can calculate the sum \sum_{j=1}^8 j, by using this known formula : \sum_{k=1}^n k=\frac{n(n+1)}{2}

    And then, you're left with only one sum, that should be easy to compute
    Last edited by Moo; April 28th 2009 at 10:21 PM. Reason: typo thanks
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor matheagle's Avatar
    Joined
    Feb 2009
    Posts
    2,763
    Thanks
    5
    Typo alert.....


    \sum_{j=1}^4 \sum_{k=2}^8 jk=\sum_{j=1}^4 \left( \sum_{k=2}^8 jk\right)
    In the second summation, since j doesn't depend on k, you can get it out from the sum :
    =\left(\sum_{j=1}^4 j\right)\left(\sum_{k=2}^8 k\right)

    or

    =\left(\sum_{k=2}^8 k\right)\left(\sum_{j=1}^4 j\right)
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Expand Double Summation
    Posted in the Advanced Applied Math Forum
    Replies: 2
    Last Post: September 6th 2011, 05:54 PM
  2. Double Summation (multiplying)
    Posted in the Discrete Math Forum
    Replies: 2
    Last Post: February 28th 2010, 08:10 PM
  3. Double Summation
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: September 20th 2009, 07:11 AM
  4. Double summation
    Posted in the Pre-Calculus Forum
    Replies: 4
    Last Post: August 23rd 2009, 06:09 PM
  5. double summation
    Posted in the Calculus Forum
    Replies: 2
    Last Post: March 30th 2009, 12:11 PM

Search Tags


/mathhelpforum @mathhelpforum