Limit of ln as x goes to infinity

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SUMMARY

The limit of the expression (ln(x))^2/x as x approaches infinity is a topic of discussion that highlights the application of L'Hôpital's Rule. Participants clarify that the limit can be rewritten as lim (ln(x))^2/x = 5/(x/ln(x)). The confusion arises from the manipulation of the limit and the introduction of an arbitrary constant, 5, which is not justified. The correct approach involves recognizing that as x approaches infinity, the term x/ln(x) also approaches infinity, leading to the conclusion that the limit evaluates to 0.

PREREQUISITES
  • Understanding of limits in calculus
  • Familiarity with L'Hôpital's Rule
  • Knowledge of logarithmic functions
  • Basic algebraic manipulation skills
NEXT STEPS
  • Study L'Hôpital's Rule in detail
  • Practice evaluating limits involving logarithmic functions
  • Explore the behavior of the function x/ln(x) as x approaches infinity
  • Review the properties of logarithms and their applications in calculus
USEFUL FOR

Students studying calculus, particularly those focusing on limits and L'Hôpital's Rule, as well as educators looking for examples to illustrate these concepts.

Cacophony
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Homework Statement


lim (lnx)^2/x
x-->infinity


Homework Equations



none

The Attempt at a Solution



=5lnx/x * (1/lnx)/(1/lnx)

=5/(x/lnx)

How do I calculate x/lnx?
 
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Cacophony said:

The Attempt at a Solution



=5lnx/x * (1/lnx)/(1/lnx)

=5/(x/lnx)

How do I calculate x/lnx?

I do not follow you. What have you done?

ehild
 
Cacophony said:

Homework Statement


lim (lnx)^2/x
x-->infinity


Homework Equations



none

The Attempt at a Solution



=5lnx/x * (1/lnx)/(1/lnx)
Where did the 5 come from? In fact, where did any of this come from? What you have makes zero sense to me.

Also, since you haven't taken the limit yet, you should not get rid of the "lim" symbol.
Cacophony said:
=5/(x/lnx)

How do I calculate x/lnx?

This is a problem that is suited to L'Hopital's Rule. Have you covered it yet?
 
Cacophony said:

Homework Statement


lim (lnx)^2/x
x-->infinity

Cacophony,

what you typed is equivalent to:

\displaystyle \lim_{x\to \infty}\dfrac{[ln(x)]^2}{x}



Did you intend

\displaystyle \lim_{x\to \infty}[ln(x)]^{\frac{2}{x}} \ ?
 

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