What is the maximum $b$ for which $\log_b(x) = \log_b(\log_b(x))$ has real solutions? And would there be 1 or 2 solutions?

31 Views Asked by At

$\log_b(x) = \log_b(\log_b(x))$

Based on preliminary observations on Desmos, $1.44<b<1.45$. For $b$ less than that, the identity has 2 real solutions, and for $b$ greater than that, it has 0 real solutions.

1

There are 1 best solutions below

1
On BEST ANSWER

$\log_b x=\log_b (\log_b x)$

iff $x=b^{\log_b x}=b^{\log_b(\log_b x)}=\log_b x$

iff $b^x=b^{\log_b x}=x$

iff $b=x^{1/x}.$

The largest value of $x^{1/x}$ occurs only when $x=e.$