## Calculus (3rd Edition)

$f(x)=9^{\tan x}$ is defined and continuous on its domain $x\in R; \ x\neq \frac{(2n+1)\pi}{2}$, $n$ is an integer.
Since $\tan x=\frac{\sin x}{\cos x}$ is defined and continuous on all $x\in R$ such that $x\neq \frac{(2n+1)\pi}{2}$, $n$ is an integer then $f(x)=9^{\tan x}$ is defined and continuous on its domain $x\in R; \ x\neq \frac{(2n+1)\pi}{2}$, $n$ is integer.