Why is [x^x^x]' NOT (xln(x)^2+ln(x)+xln(x)+1)*x^(x+x^x)?

  • Context: Undergrad 
  • Thread starter Thread starter NotASmurf
  • Start date Start date
Click For Summary

Discussion Overview

The discussion revolves around the differentiation of the function \( y = x^{x^{x}} \). Participants explore various methods of applying the chain rule and express confusion over differing results from computational tools like Mathematica, Symbolab, and Wolfram Alpha. The focus is on the theoretical and technical aspects of differentiation in this context.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant outlines their differentiation process using the chain rule, expressing uncertainty about the correctness of their result compared to outputs from computational tools.
  • Another participant questions the representation of \( x^{x^{x}} \) and suggests that it could be expressed as \( (x^x)^{(x^x)} \), indicating a potential misunderstanding in the function's structure.
  • A later reply acknowledges a mistake in interpreting the function and thanks another participant for pointing it out, suggesting that clarity in notation is crucial for differentiation.
  • Some participants express agreement with the differentiation approach but differ on specific factors, particularly regarding the presence of \( e^{(x^{(x^x)})} \) in the final expression.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct differentiation of \( y = x^{x^{x}} \), with multiple competing views and interpretations of the function's structure and differentiation process remaining unresolved.

Contextual Notes

There are limitations in the discussion regarding the clarity of notation and the assumptions made about the function's form, which may affect the differentiation process. The reliance on computational tools without access to intermediary steps also contributes to the uncertainty.

NotASmurf
Messages
150
Reaction score
2
Mathamatica, Symbolab, manual differentiation all return diffrent forumals, I cannot see wolfram's intermediary steps, symbolab's intermediary steps seem like they're treating a function like a constant and I can't trust my work when everything else disagrees, but i don't see where my logic would falter as long as x^x^x can be represented by f(x) = x^x, g(x) = x^x, x^x^x = f(g(x))

$$\frac{dy}{dx} of y = e^x^x $$ is

y = e^x^x

y' = q(g(x))' = q'(g(x))*g'

g(x) = x^x, q(x) = e^x
g'(x) = (ln(x) + 1)*x^x, q'(x) = e^x

y' = e^x^x * (ln(x) + 1)*x^x

y' = x^x * (ln(x) + 1)*e^x^x

The above is correct, dy/dx x^x was obtained via:
g(x) = x^x
ln(g) = xln(x)
ln(g)' = (xln(x))'
ln(g)' = 1 * ln(x) + x * 1/x
g'/g = 1 * ln(x) + x * 1/x
g'/g = ln(x) + 1
g' = (ln(x) + 1)*x^x

But when i try continue for e^x^x^x via chain rule
t=x^x^x = f(g(x))
f=x^x g = x^x
f' = (ln(x) + 1)*x^x, g' = (ln(x) + 1)*x^x

(f(g(x)))' = f'(g(x))*g'(x) = (ln(x) + 1)(ln(x^x) + 1)*x^x^x * x^x = (xln(x)^2 + ln(x) + xln(x) + 1) * x^(x + x^x)

dy/dx x^x^x = (xln(x)^2 + ln(x) + xln(x) + 1) * x^(x + x^x)

I obtain the incorrect answer, as wolfram says dy/dx of x^x^x = e^x^x^x * (xln(x)^2 + xln(x) + 1) * x^(x + x^x -1), but I do not have the professional version of wolfram, thus I cannot see the intermediary steps, and cannot find this information anywhere else,

Any help appreciated.
 
Last edited:
Physics news on Phys.org
NotASmurf said:
i don't see where my logic would falter as long as x^x^x can be represented by f(x) = x^x, g(x) = x^x, x^x^x = f(g(x))
If f(x) = g(x) = ##x^x## then f(g(x)) = ##g(x)^{g(x)}## = ##(x^x)^{(x^x)}##
 
ah, damn, should have noticed that. Thanks so much.
 
How would i make it into a chain rule form? x^x^x not (x^x)^(x^x)?
 
NotASmurf said:
How would i make it into a chain rule form? x^x^x not (x^x)^(x^x)?
For ## dy/dx ## where ## y=x^{(x^x)} ##, I do not get the answer you quoted from Wolfram, but the calculation should be straightforward. Write ## y=x^{(x^x)} ## and take the natural twice on both sides of the equation. Then simply apply the chain rule and implicit differentiation of both sides and solve for ## dy/dx ##. ## \\ ## In fact I am in agreement with what you quoted from Wolfram other than the factor ## e^{(x^{(x^x)})} ## which I have as simply being 1.
 
Charles Link said:
For ## dy/dx ## where ## y=x^{(x^x}) ##, I do not get the answer you quoted from Wolfram, .

I checked with a knowingly working tetration differentiation formula, although berkeman pointed out , my mistake was that what I typed as x^x^x is actually (x^x)^(x^x). Thanks though.
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 15 ·
Replies
15
Views
4K
  • · Replies 5 ·
Replies
5
Views
1K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 17 ·
Replies
17
Views
4K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 8 ·
Replies
8
Views
1K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 9 ·
Replies
9
Views
3K