Small problem understanding application of chain rule

Click For Summary
SUMMARY

The discussion centers on the application of the chain rule in calculus, specifically regarding the derivative of the natural logarithm of the absolute value function. The user correctly identifies that the derivative of ln|x| is 1/x but struggles with the application of the general rule \(\frac{d}{dx} ln(u) = \frac{u'}{u}\) and the derivative of |x|. The user’s calculation leads to \(\frac{x}{|x|^{2}}\), which is incorrect due to a misunderstanding of the absolute value function's behavior in the context of derivatives. The correct derivative of ln|x| is indeed \(\frac{1}{x}\), as the absolute value does not affect the derivative in this case.

PREREQUISITES
  • Understanding of basic calculus concepts, particularly derivatives
  • Familiarity with the chain rule in differentiation
  • Knowledge of the properties of absolute values in mathematical functions
  • Experience with logarithmic functions and their derivatives
NEXT STEPS
  • Study the chain rule in calculus with a focus on composite functions
  • Review the properties of absolute value functions and their derivatives
  • Practice differentiating logarithmic functions, including ln|u|
  • Explore common pitfalls in calculus to avoid similar mistakes in differentiation
USEFUL FOR

Students studying calculus, educators teaching differentiation techniques, and anyone looking to deepen their understanding of logarithmic derivatives and the chain rule.

K29
Messages
103
Reaction score
0

Homework Statement


I have proven in two ways (correctly) that the derivative of ln|x| = 1/x (note absolute value does vanish)

Now I open my textbook and see a general rule that [tex]\frac{d}{dx} ln (u) = \frac{u'}{u}[/tex]

And the not so general derivative of |x| is [tex]\frac{d}{dx} |x| = \frac{x}{|x|}[/tex]

So using these statements [tex]\frac{d}{dx} ln (|x|) = \frac{|x|'}{|x|}[/tex]
[tex]=\frac{(\frac{x}{|x|})}{|x|}[/tex]
[tex]=\frac{x}{|x|^{2}}[/tex]

I've looked over this a few times and I can't see what I've done wrong. I mean I'm looking for a silly mistake but I don't see it. Can you see where I've gone wrong? Whats going on here?
 
Last edited:
Physics news on Phys.org
abs(x)^2 = x^2
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 10 ·
Replies
10
Views
2K
Replies
2
Views
2K
  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
2
Views
2K