Methods used by analogy, for example $x ^ x = 3 ^ 3 \implies x = 3$,

Determine the value of $x$ in $$M ^ {M ^ M} = x ^ {1 / (x-1)}$$ if $M = 5 ^ {\sqrt{5} / 10}$.

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    $\begingroup$ Maple answers $x=2.55849460788022014674343500422 $. $\endgroup$ – user64494 Aug 12 '15 at 19:03
  • $\begingroup$ I think a good starting point is to recognize that $M$ can be written as $\sqrt{5}^{\frac{1}{\sqrt{5}}}$ $\endgroup$ – 1-___- Aug 12 '15 at 19:21

I'm not entirely sure how you're supposed to spot the solution here, but one may solve this equation for $x$ using the Lambert W function as follows:



which admits two different real solutions. Since $-\ln(C)/C=\ln(1/C)e^{\ln(1/C)}$, one of these solutions simplifies down to $x=1$, which is an extraneous solution. The other is non-trivial and may simplify, though it is not obvious to me.

  • $\begingroup$ Do you think the question is a PSQ? If you do then try not to give a full answer, even though I see that you've been quite into the Lambert W function lately :) $\endgroup$ – TheSimpliFire Aug 12 '18 at 16:08
  • $\begingroup$ @TheSimpliFire I do, though it's old and I'm trying to remove it from the unanswered list. (One may also wish to see the OP's profile) $\endgroup$ – Simply Beautiful Art Aug 12 '18 at 16:10
  • $\begingroup$ Mhm... In any case do as you wish with them. $\endgroup$ – Simply Beautiful Art Aug 12 '18 at 16:12

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