Results 1 to 18 of 18

Thread: annoying sigma problem

  1. #1
    princeso Kirby's Avatar
    Join Date
    Mar 2009
    Posts
    19,082

    Default annoying sigma problem

    I have done it a few times, but I can't seem to get the right answer:

    Limit n-> infinity : nE(i=1)_(1+(2i)/n)^2*(2/n)

    here is my best attempt:

    (limit in front for all of this)
    1. move the 2/n over to get: 2/n*(nE(i=1)_(1+(2i)/n)^2)
    2. foil to get: 2/n*(nE(i=1)_(1+4i/n+4i^2/n^2)
    3. break it put into further sigma: 2/n*(nE(i=1)_1+nE(i=1)_4i/n+nE(i=1)_4i^2/n^2)
    4. move over shit: 2/n*(nE(i=1)_1+(4/n)*nE(i=1)_i+(4/n^2)*nE(i=1)_i^2)
    5. simplify the sigmas: 2/n*(n+(4/n)*((n)(n+1)/2)+(4/n^2)*((n)(n+1)(2n+2))/6))
    6. simplifying: 2/n*(n+2(n+1)+(2*(n+1)(2n+2)/(3*n)))

    at this point I am not quite sure what to do to be honest, I am not sure how to simplify the 3rd term more tied in with the front 2/n

    any ideas?

  2. #2
    Registered Users Regular Flaming Flamingo's Avatar
    Join Date
    Jan 2012
    Posts
    515

    Default

    That looks complicated.

  3. #3
    what about .. eyebrows God's Avatar
    Join Date
    Apr 2005
    Location
    among the people
    Posts
    49,777

    Default

    i dont know what you're talking about?

    are the E's supposed to be summation signs? who calls them sigmas? ill try to make sense of how you're writing the notation.

  4. #4
    princeso Kirby's Avatar
    Join Date
    Mar 2009
    Posts
    19,082

    Default

    lol yes they are summation, I call them sigmas

  5. #5
    Registered Users Regular Rayne's Avatar
    Join Date
    Mar 2009
    Posts
    8,588

    Default

    (4/3)n^2 + 4n + 6

  6. #6
    Registered Users Regular Rayne's Avatar
    Join Date
    Mar 2009
    Posts
    8,588

    Default

    assuming i interpreted that clusterfuck of a problem correctly

  7. #7
    Registered Users Regular Rayne's Avatar
    Join Date
    Mar 2009
    Posts
    8,588

    Default

    what the fuck

  8. #8
    Registered Users Regular Rayne's Avatar
    Join Date
    Mar 2009
    Posts
    8,588

    Default

    hold the fuck up kirby, is this the problem?

    lim n->infinity, summation from i=1 to n of ((1+(2i/n))^2) * (2/n)

  9. #9
    what about .. eyebrows God's Avatar
    Join Date
    Apr 2005
    Location
    among the people
    Posts
    49,777

    Default

    uh what are the limits of summation. i=1 to infinity? whats does the n in front of the sum mean, a constant?

  10. #10
    princeso Kirby's Avatar
    Join Date
    Mar 2009
    Posts
    19,082

    Default

    yeah

  11. #11
    Registered Users Regular Rayne's Avatar
    Join Date
    Mar 2009
    Posts
    8,588

    Default

    he means the n is on top of the sigma which he represents by E. so its i=1 to n.

  12. #12
    Registered Users Regular Rayne's Avatar
    Join Date
    Mar 2009
    Posts
    8,588

    Default

    Quote Originally Posted by Kirby View Post
    yeah
    ok hold on

  13. #13
    princeso Kirby's Avatar
    Join Date
    Mar 2009
    Posts
    19,082

    Default

    Quote Originally Posted by God View Post
    uh what are the limits of summation. i=1 to infinity? whats does the n in front of the sum mean, a constant?
    basically 1 to infinity, the n works for the format for some reason, basically at the end of this problem you substitute infinity to n

    in reality the problem looks like this
    ...................................n
    lim .............................E........the problem
    n->infinity ...................i=1

  14. #14
    Registered Users Regular Rayne's Avatar
    Join Date
    Mar 2009
    Posts
    8,588

    Default

    26/13

  15. #15
    princeso Kirby's Avatar
    Join Date
    Mar 2009
    Posts
    19,082

    Default

    it says no

  16. #16
    Registered Users Regular Rayne's Avatar
    Join Date
    Mar 2009
    Posts
    8,588

    Default

    fuck i meant 26/3

  17. #17
    what about .. eyebrows God's Avatar
    Join Date
    Apr 2005
    Location
    among the people
    Posts
    49,777

    Default

    i havent done a sum problem in a while but just with some preliminary scribbling, is it just 4?

  18. #18
    princeso Kirby's Avatar
    Join Date
    Mar 2009
    Posts
    19,082

    Default

    rayne got it

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •