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L'Hopitals Rule

  1. Dec 5, 2006 #1
    Can one use L'Hopital's Rule on the indeterminate form (-∞)/∞ ?

    And by the way, is there a way to write mathematical signs like ∞, the integral sign etc except google-ing, cutting and pasting?
    Last edited: Dec 5, 2006
  2. jcsd
  3. Dec 5, 2006 #2
    I think you can. It would probably be:

    [tex] -\lim_{x\rightarrow c} \frac{f(x)}{g(x)} [/tex] so that both functions approach [tex] \infty [/tex]

    you write those signs in [tex] tags as follows: \infty \int
    Last edited: Dec 5, 2006
  4. Dec 5, 2006 #3
    Yes, it's a french name. But that doesn't really help me a lot :tongue2:
  5. Dec 5, 2006 #4
    OK, thanks!
  6. Dec 5, 2006 #5
    I'm not sure, I think its only 0/0, as it comes from the Taylor expansion about the point that x approaches, ie.

    [tex]\lim_{x\rightarrow a}\frac{f(x)}{g(x)} = \lim_{x\rightarrow a}\frac{f(a) + f'(x)(x-a) + ...}{g(a) + g'(x)(x-a) + ...} = \lim_{x\rightarrow a}\frac{f'(x)}{g'(x)}[/tex]

    With f(a)=g(a)=0

    Something like that anyway.
  7. Dec 5, 2006 #6
    No you can use L'Hopitals Rule for indeterminate forms, not just 0/0.
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