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Homework Help: Limit using l'hopitals rule

  1. Jan 17, 2010 #1
    1. The problem statement, all variables and given/known data
    Find the limit as x goes to 1 of tan(pi*x/2)lnx

    2. Relevant equations
    using l'hopitals, lim f'(x)/g'(x)=answer

    3. The attempt at a solution
    i tried integrating by making the tangent part squared so i can divide by the tangent part, but i keep getting stuck. i think the answer is either 1 or infinity.

    help please? thanks
  2. jcsd
  3. Jan 17, 2010 #2


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    Science Advisor
    Homework Helper

    I really don't know how you are trying to do the problem. l'Hopital's rule doesn't tell you to integrate anything. Write it as ln(x)/cot(pi*x/2). Now it's a 0/0 form. Now differentiate numerator and denominator like l'Hopital says.
  4. Jan 17, 2010 #3
    woops i meant taking the derivative
  5. Jan 17, 2010 #4


    Staff: Mentor

    Integrating has nothing to do with this problem. Try rewriting your limit as
    [tex]\lim_{x \to 1}\frac{ln(x)}{cot(x*\pi/2)}[/tex]

    Now you have something you can use L'Hopital's Rule on.
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