1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Limit question (inf. - inf.)

  1. Feb 8, 2005 #1

    mad

    User Avatar

    EDITED THE EQUATION


    Hello all,

    I have this problem I can't solve.. it is a infinite - infinite. I tried it around 5 times and can't find the correct answer (infinite). I'm pretty sure I have to put in evidence x^2 and use a limit law but I can't find the answer.. can someone help me for this problem:

    lim x -> +inf. [tex] x - \ln(x^2-1) [/tex]

    Thanks very much in advance.
     
    Last edited: Feb 8, 2005
  2. jcsd
  3. Feb 8, 2005 #2
    The limit evaluates to -0.5? How do you know this?

    --J
     
  4. Feb 8, 2005 #3

    mad

    User Avatar

    That's the answer in the book =)

    Sorry, it was x - (lnx^2-1)
     
    Last edited: Feb 8, 2005
  5. Feb 8, 2005 #4
    x^2 increases much faster than ln(x^2 -1). The limit should be unbounded.

    The technique I'd use to evaluate it would be to write x^2 as [itex]\ln{\left(e^{x^2}\right)}[/tex] and then combine the logs. This approach gives a result of infinity, as well.

    --J
     
  6. Feb 8, 2005 #5

    mad

    User Avatar

    I edited the equation. It was a typo.. sorry
     
  7. Feb 8, 2005 #6
    [tex]x - \left(\ln{x^2}\right) - 1[/tex]
    or
    [tex]x - \ln{(x^2 -1)}[/tex]
    ?

    Well, either way, the limit is still unbounded.

    --J
     
  8. Feb 8, 2005 #7

    mad

    User Avatar

    This one. I will try your method. Is it the only way?
     
  9. Feb 8, 2005 #8
    Heh, I screwed up the notation, too. I edited to give the proper two possibilities. As it was before, they said exactly the same thing!

    --J
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Limit question (inf. - inf.)
  1. Limit question (Replies: 6)

  2. Limit question (Replies: 6)

  3. Limit question (Replies: 4)

  4. A Limits Question (Replies: 3)

  5. Limits Question (Replies: 1)

Loading...