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

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  • Thread starter NotASmurf
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In summary, 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))
  • #1
NotASmurf
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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.
 
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  • #2
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)}##
 
  • #3
ah, damn, should have noticed that. Thanks so much.
 
  • #4
How would i make it into a chain rule form? x^x^x not (x^x)^(x^x)?
 
  • #5
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.
 
  • #6
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.
 

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

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

The expression [x^x^x]' is not equivalent to (xln(x)^2+ln(x)+xln(x)+1)*x^(x+x^x) because the two expressions have different derivative forms. The first expression, [x^x^x]', is the derivative of x^x^x, while the second expression is a product of two functions, f(x) = (xln(x)^2+ln(x)+xln(x)+1) and g(x) = x^(x+x^x). These two functions have different derivatives, and thus the two expressions are not equivalent.

2. How do you differentiate the expression [x^x^x]'?

The expression [x^x^x]' can be differentiated using the chain rule. First, we can rewrite x^x^x as e^(x^ln(x)). Then, we can apply the chain rule to find the derivative, which is x^x^x * (ln(x) + 1 + xln(x)).

3. What is the derivative of x^(x+x^x)?

The derivative of x^(x+x^x) can be found using the product rule. The first function is f(x) = x and the second function is g(x) = x+x^x. The derivative is then f'(x) * g(x) + f(x) * g'(x), which simplifies to (1 + xln(x)) * x^(x+x^x).

4. Can the two expressions be simplified or rewritten to be equivalent?

No, the two expressions cannot be simplified or rewritten to be equivalent. The first expression is the derivative of a power function, while the second expression is a product of two functions. These two forms are not equivalent and cannot be simplified or rewritten to be equal.

5. Are there any values of x for which the two expressions are equal?

No, there are no values of x for which the two expressions are equal. As mentioned before, the two expressions have different derivative forms and cannot be simplified to be equivalent. Therefore, there are no values of x for which the two expressions would be equal.

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