Limit using l'hopitals rule

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Remember that cot(1*pi/2) = cot(\pi/2) is undefined.In summary, to find the limit as x goes to 1 of tan(pi*x/2)lnx, you can rewrite it as ln(x)/cot(pi*x/2) and use l'Hopital's rule to find the answer. Remember to be careful with undefined values.
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magnifik
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Homework Statement


Find the limit as x goes to 1 of tan(pi*x/2)lnx


Homework Equations


using l'hopitals, lim f'(x)/g'(x)=answer


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
 
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  • #2
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.
 
  • #3
woops i meant taking the derivative
 
  • #4
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.
 

1. What is l'Hopital's rule?

L'Hopital's rule is a mathematical technique used to evaluate the limit of a function that is in an indeterminate form, such as 0/0 or ∞/∞.

2. When should l'Hopital's rule be used?

L'Hopital's rule should only be used when the limit of a function cannot be evaluated using other methods, such as direct substitution or factoring.

3. How does l'Hopital's rule work?

L'Hopital's rule states that for a function f(x)/g(x), where both f(x) and g(x) approach 0 or ∞ as x approaches a certain value, the limit of the function is equal to the limit of the derivative of f(x) divided by the derivative of g(x). This can be applied repeatedly until the limit can be evaluated.

4. What are the limitations of l'Hopital's rule?

L'Hopital's rule can only be used for limits involving functions that have a well-defined derivative. It cannot be used for limits involving discontinuous functions or functions with vertical asymptotes.

5. Are there any alternatives to using l'Hopital's rule?

Yes, there are other methods for evaluating limits such as direct substitution, factoring, and using trigonometric identities. It is important to try these methods first before resorting to l'Hopital's rule.

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