Results 1 to 18 of 18

Thread: annoying sigma problem

  1. #1
    princeso Kirby's Avatar
    Join Date
    Mar 2009
    Posts
    19,117

    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
    49,802

    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.
    "I'll go," said Chagataev. "But what will I do there? Build socialism?"
    "What else?" said the secretary.

  4. #4
    princeso Kirby's Avatar
    Join Date
    Mar 2009
    Posts
    19,117

    Default

    lol yes they are summation, I call them sigmas

  5. #5
    Registered Users Regular Rayne's Avatar
    Join Date
    Mar 2009
    Posts
    8,610

    Default

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

  6. #6
    Registered Users Regular Rayne's Avatar
    Join Date
    Mar 2009
    Posts
    8,610

    Default

    assuming i interpreted that clusterfuck of a problem correctly

  7. #7
    Registered Users Regular Rayne's Avatar
    Join Date
    Mar 2009
    Posts
    8,610

    Default

    what the fuck

  8. #8
    Registered Users Regular Rayne's Avatar
    Join Date
    Mar 2009
    Posts
    8,610

    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
    49,802

    Default

    uh what are the limits of summation. i=1 to infinity? whats does the n in front of the sum mean, a constant?
    "I'll go," said Chagataev. "But what will I do there? Build socialism?"
    "What else?" said the secretary.

  10. #10
    princeso Kirby's Avatar
    Join Date
    Mar 2009
    Posts
    19,117

    Default

    yeah

  11. #11
    Registered Users Regular Rayne's Avatar
    Join Date
    Mar 2009
    Posts
    8,610

    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
    8,610

    Default

    Quote Originally Posted by Kirby View Post
    yeah
    ok hold on

  13. #13
    princeso Kirby's Avatar
    Join Date
    Mar 2009
    Posts
    19,117

    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
    8,610

    Default

    26/13

  15. #15
    princeso Kirby's Avatar
    Join Date
    Mar 2009
    Posts
    19,117

    Default

    it says no

  16. #16
    Registered Users Regular Rayne's Avatar
    Join Date
    Mar 2009
    Posts
    8,610

    Default

    fuck i meant 26/3

  17. #17
    what about .. eyebrows God's Avatar
    Join Date
    Apr 2005
    Location
    among the people
    Posts
    49,802

    Default

    i havent done a sum problem in a while but just with some preliminary scribbling, is it just 4?
    "I'll go," said Chagataev. "But what will I do there? Build socialism?"
    "What else?" said the secretary.

  18. #18
    princeso Kirby's Avatar
    Join Date
    Mar 2009
    Posts
    19,117

    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
  •