Why Does l'Hospital's Rule Fail for lim(x→0^+) (lnx/x)?

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SUMMARY

The limit lim(x→0^+)(lnx/x) approaches -∞, as ln(x) approaches -∞ when x approaches 0 from the right. The expression cannot be simplified using l'Hospital's Rule because the conditions for its application are not met. Specifically, the limit involves a product of terms where one approaches infinity and the other approaches negative infinity, leading to an indeterminate form. Therefore, the correct evaluation of the limit is achieved by recognizing the behavior of ln(x) and the reciprocal of x as x approaches 0.

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Homework Statement



lim(x→0^+)(lnx/x)


The Attempt at a Solution


First, what does x->0+ mean? Is it positive infinity?
Why lim(x→0^+) (lnx)=-∞?
Why the answer is

= -∞ * (1/0+)
= -∞* ∞
= -∞?
Why cannot I use l'Hospital Rule?
 
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phillyolly said:

Homework Statement



lim(x→0^+)(lnx/x)


The Attempt at a Solution


First, what does x->0+ mean? Is it positive infinity?
It means that x approaches zero from the right (positive values close to zero).
phillyolly said:
Why lim(x→0^+) (lnx)=-∞?
Look at the graph of y = ln(x). The domain is {x | x > 0}. As x gets closer to zero, y gets more and more negative.
phillyolly said:
Why the answer is

= -∞ * (1/0+)
= -∞* ∞
= -∞?
What you have above is mostly incorrect. 1/0 is not a number, so you can't use it in calculations. \lim_{x \to 0^+} \frac{ln(x)}{x} = \lim_{x \to 0^+} \frac{1}{x}ln(x)
The first factor gets larger and larger without bound; the second factor gets more and more negative without bound. As a result the product's limit is -∞.
phillyolly said:
Why cannot I use l'Hospital Rule?
Read the fine print in L'Hopital's Rule. There are certain conditions that must be satisfied before you can use it.
 
That's a great explanation. Thank you a lot.
 

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