# Power tower(infinite tetration) [duplicate]

How to find the domain and range of $$Y=x^{x^{x^{x^{x^{...}}}}}=x^Y$$

I know how to differentiate the function. I don't know how to proceed further.

We should prove that domain:$$[1/(e^e),e^{(1/e)}]$$ and range:$$[1/e,e]$$

As you said: $$y=x^y$$ and so: $$\ln(y)=y\ln(x)$$ $$\ln(x)=\frac{\ln(y)}{y}\tag{1}$$ now if we take: $$L_1=\lim_{y\to\infty}\frac{\ln(y)}{y}=\lim_{y\to\infty}\frac{1}{y}=0$$ If you mean for a given domain that is the range, we can work backwards from $$(1)$$ to get the domain from the range. Differentiating we get: $$\frac1x=\left(\frac{1}{y^2}-\frac{\ln(y)}{y^2}\right)\frac{dy}{dx}$$ $$\frac{dy}{dx}=\frac{y^2}{x(1-\ln y)}$$ so our minimum/maximum will occur when $$y=0$$, but to work out $$x$$ you must evaluate: $$x=\exp\left(\lim_{y\to0}\frac{\ln(y)}{y}\right)$$