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Can this limit be computed?

  1. Sep 15, 2012 #1
    I've been trying for a while to compute this limit. Is there even a unique solution to this problem?

    [tex] \lim_{x→∞} x^{1-p} [/tex] where [itex] p>1 [/itex]

    I tried using L'Hopital's rule, but it didn't work out.

  2. jcsd
  3. Sep 15, 2012 #2
    I'm also curious about the answer

    lim(x-->∞) x1-p = lim(x-->∞) x1x-p = lim(x-->∞) x/xp = ∞/∞

    So we apply L'hopitals:

    lim(x-->∞) 1/(pxp-1) = 1/p lim(x-->∞) 1/(xp-1)

    so as long as p-1>0 the limit goes to 0, right? And we know, p>1, so we know that p-1>0 so this should go to 0
  4. Sep 15, 2012 #3
    It seems to me that, intuitively, your function should approach zero regardless of p (assuming p > 1). Let me see what I can do more legitimately though.

    First split ##x^{1-p}## into ##x^1 x^{-p}##

    From there I would make it a quotient and try some fancy l'hopital's on it. I'd help more but I need to get somewhere. Good luck, however!

    Mod note: in LaTeX expressions with exponents with more than one character, use braces - {} - around the exponent. I fixed the exponents above.
    Last edited by a moderator: Sep 15, 2012
  5. Sep 15, 2012 #4


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    1. Do you know in which cases you're allowed to use L'Hôpital's rule ??
    2. By [itex] \infty [/itex] do you assume [itex] +\infty [/itex] ?
    2. If p>1, then 1-p <0 = -s, s>0, so that the object under the limit becomes

    [tex] \frac{1}{x^s}, ~ s>0 [/tex]

    Which should be easier to handle when considering the limit.
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