I'm trying to show that $\log_{a}(n) \in \theta(\log_{b}(n))$ with $a,b > 0$
To prove it, I use the 'limit' theorem :
$g \in \theta(f) \Leftrightarrow \lim_{n \to +\infty} \frac{g(n)}{f(n)}=c$ with $c$ real constant. But after that, I get $\log_a$ over $\log_b$ and I don't know how to go on...