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I solved the following equation by inspection and also by graphing (Desmos). x = 1. Is it possible to put this equation into Lambert form? I tried but could not do it. Thanks. $$ 2^x = x + 1/x $$

gt6989b
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Frederick
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1 Answers1

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$$2^x=x+\frac{1}{x}$$

$$e^{\ln(2)x}=x+\frac{1}{x}$$

$$\frac{x}{x^2+1}e^{\ln(2)x}=1$$

One real solution is $x=1$.

We see, your equation cannot be solved in terms of Lambert W. But it is solvable in terms of Generalized Lambert W:

$$x=\frac{1}{\ln(2)}W\left(^{\ \ \ \ \ \ \ \ \ \ \ 0}_{-\ln(2)i,\ln(2)i};\frac{1}{\ln(2)}\right)=-\frac{1}{\ln(2)}W\left(^{-\ln(2)i,\ln(2)i}_{\ \ \ \ \ \ \ \ \ \ \ 0} ;\ln(2)\right)$$

$-$ see the references below.
$\ $

[Mezö 2017] Mezö, I.: On the structure of the solution set of a generalized Euler-Lambert equation. J. Math. Anal. Appl. 455 (2017) (1) 538-553

[Mezö/Baricz 2017] Mezö, I.; Baricz, A.: On the generalization of the Lambert W function. Transact. Amer. Math. Soc. 369 (2017) (11) 7917–7934 (On the generalization of the Lambert W function with applications in theoretical physics. 2015)

[Castle 2018] Castle, P.: Taylor series for generalized Lambert W functions. 2018

IV_
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  • Thank you very much, IV_. This is why I post things on StackExchange: Some people are higher on the learning curve than I. (LOL). Thanks, again. Fred – Frederick Apr 18 '22 at 21:03
  • @Frederick Solution theory for usual equations and inverses seems to be not so well known. There is a beginning of a solution theory for the elementary functions: https://math.stackexchange.com/questions/154769/is-there-a-general-way-to-solve-transcendental-equations/2368151#2368151 To my knowledge, there is no proof theory that can decide if a given equation can be solved in terms of Lambert W or not. – IV_ Apr 19 '22 at 16:16
  • Thanks, again for the education/information. – Frederick Apr 21 '22 at 13:11