Ask Me Help Desk

Ask Me Help Desk (https://www.askmehelpdesk.com/forum.php)
-   Mathematics (https://www.askmehelpdesk.com/forumdisplay.php?f=199)
-   -   Limit with sinsinsin. (https://www.askmehelpdesk.com/showthread.php?t=378059)

  • Jul 21, 2009, 06:38 AM
    Nivg
    Limit with sinsinsin.
    Hi all,

    http://i42.photobucket.com/albums/e3...nofalfears.gif

    I'm trying to figure how to do that one, the only thing that cross my mind is something with sandwiched, any hint, thought or help about this one will be most grateful.
  • Jul 21, 2009, 03:23 PM
    galactus
    Is this an infinite product or nested sines? I just want to be sure what you mean.

    Is it:



    Or are they nested like so:

    I am confused by the 'n times'. Does the 'n times' represent how many times sin occurs.

    Regardless, since n is the limiting factor and , it would appear the limit approaches 0 as

    Is this the exact way it is presented to you?

    Just making sure.
  • Jul 22, 2009, 06:53 AM
    Nivg

    they nested sins (n represent how many times sin occurs), and I know the limit = 0, as it's easy to check this one with computer, I just don't know how to prove it.
  • Jul 22, 2009, 07:05 AM
    galactus
    It is just a matter of observation. X is not the limiting factor. As n gets larger and larger, it goes to 0 because of the n in the denominator.

    It essentially the same as proving

    and x is a constant. Say x=1.

  • Jul 22, 2009, 07:17 AM
    Nivg

    Maybe I mislead you or misunderstood you there is no "n" in the denominator, there is no denominator, it's :

    lim (sin(sin(sin... sin(x)))), as n->inf

    n it's the number of times you get this sin inside sin thing.
  • Jul 22, 2009, 10:12 AM
    Unknown008

    Well, you post seemed to me too that there was a denominator 'n' in your expression... *looks up again* yes, there is a denominator.
  • Jul 22, 2009, 10:45 AM
    Nivg

    I will use another font next time, again there is no denominator, sorry for misleading you people, now when we cleared this up what with some help here :P.

    * lim (sin(sin(sin... sin(x)))), as n->inf

    n it's the number of times you get this sin inside sin thing.
  • Jul 22, 2009, 03:36 PM
    galactus
    This is not very rigorous, but it may suffice. By letting



    We then note that:



    Then we have

    The value that satisfies this is L=0
  • Jul 22, 2009, 04:02 PM
    Nivg

    you say the series [x,sinx,sin(sinx),. ] is continues and monotone decreasing in [0,pi] or monotone increasing in [-pi,0] so limXn = limXn+1=L, meaning sinL=L and that only works when L=0, right?
    that what you are saying?
  • Jul 24, 2009, 12:24 PM
    galactus
    Yes. It is monotone decreasing and bounded below. You can show the limit exists by proving this if you wish.

    You may want to prove the limit sin(L)=L rigorously.
  • Jul 24, 2009, 11:30 PM
    Nivg

    OK thanks for all the help I got my answer :P

  • All times are GMT -7. The time now is 03:59 AM.