How Can You Explore Solutions for ln() with Negative Values?

  • Context: Graduate 
  • Thread starter Thread starter Alkatran
  • Start date Start date
Click For Summary

Discussion Overview

The discussion revolves around the exploration of the natural logarithm function, specifically addressing the implications of applying the logarithm to negative values and the potential for complex solutions. Participants examine the mathematical relationships and identities involving ln(x) and ln(-x).

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant claims that 1/ln(x) equals ln(-x), suggesting a relationship between the logarithm of negative values and the reciprocal of the logarithm.
  • Another participant corrects this by stating that ln(x)^-1 does not equal ln(-x) and points out the correct identity ln(1/x) = -ln(x).
  • A further contribution clarifies that ln(-x) can be expressed as ln(-1) + ln(x), indicating that there are complex solutions but none on the real line.
  • A later reply acknowledges a misunderstanding related to the equation -x = 1/x, indicating a realization of an error in reasoning.

Areas of Agreement / Disagreement

Participants express disagreement regarding the initial claim about the relationship between ln(x) and ln(-x). There is no consensus on the correct interpretation of logarithmic identities involving negative values, and the discussion remains unresolved.

Contextual Notes

Limitations include the dependence on the definitions of logarithmic functions and the distinction between real and complex solutions, which are not fully explored in the discussion.

Alkatran
Science Advisor
Homework Helper
Messages
959
Reaction score
0
1/ln(x) = ln(x)^-1 = ln(-x)
ln(-e) = 1/ln(e) = 1/1 = 1

ln() is only defined over positive values, but you can find solutions like so... where's the error.
 
Physics news on Phys.org
ln(x)^-1 = ln(-x) is incorrect. You're probably thinking of ln (1/x) = - ln (x)
 
Your trouble is that

[tex]\ln (-x) \ne (\ln(x))^{-1})[/tex]
This is the correct way to do it.
[tex]\ln (-x) = \ln(-1 * x) = \ln(-1) + \ln(x)[/tex]


There will be complex solutions to this but none on the Real line.
 
Thanks, I knew something wasn't right. I should caught on when -x = 1/x :smile:
 

Similar threads

  • · Replies 7 ·
Replies
7
Views
4K
  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 12 ·
Replies
12
Views
3K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 6 ·
Replies
6
Views
2K