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Let $f$ be a function such that :$f:\mathbb{R+}\to \mathbb{R+}$ and $f^{-1}$ is a compositional inverse of $f$ , I have tried to find solution of the following functional $f(x)^{f^{-1}(x)}=x^2$, I took $f(x)=x$ but it doesn't work it coincide only for $x=1$ and for $f(x)=\exp(x)$ I come up to $x^x=x^2$ then coincide only for $x=1$ and $x=2$ , so $f(x)^{f^{-1}(x)} > x$ for $x >2$ which means no trivial solution exists probably a formel power series exist arround $x=1$ or $x=2$,Then my question here is : How I can solve $f(x)^{f^{-1}(x)}=x^2$ with $ f^{-1}$ is a compositional inverse of $f$ ?

Edit I suspect such trigonometric function would be works for the titled function,like $\tan x$ as shown here but this need a restriction of our Domain of definitions for which $\tan x$ to be defined

Edit I have edited the question according to the answer given by @Robert I without changing the meaning I missed that I search about a real valued function not complex as stated in the below answer

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When $f(x) < 0$ (which must happen for uncountably many $x$ if $f^{-1}$ is defined on $\mathbb R$), the fact that $f(x)^{f^{-1}(x)} > 0$ requires $f^{-1}(x)$ to be a rational number (presuming we define $a^b = \exp(b \log(a))$ for some branch of the logarithm; note all branches of logarithm of a negative number have imaginary part an integer multiple of $\pi i$, and $\exp(b k \pi i)$ is a positive real only when $b k$ is an even integer). Since $f$ can't map a countable set onto an uncountable one, we conclude there is no such function.

Or did you want to just define $f$ and $f^{-1}$ on $(0,\infty)$?

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  • $\begingroup$ I think this answer, while correct, won't satisfy the OP. He clearly knows nothing about complex numbers. This is $\sim$ 10th such question of the OP in the last 10 days. $\endgroup$
    – user6976
    Commented Apr 14, 2020 at 13:24
  • $\begingroup$ @MarkSapir, we are learn from you ,and i don't know if it is not allowed in MO to ask for one day with one question, I have many related research this is the reason let me ask every day , In anyway thanks for your attention $\endgroup$ Commented Apr 14, 2020 at 14:35
  • $\begingroup$ The question changed and the answer no longer applies. Now the OP should learn the notion of continuous function and change the question again. $\endgroup$
    – user6976
    Commented Apr 14, 2020 at 22:25

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