## Calculus (3rd Edition)

$f(x)=\tan^2 x$ is contiuous on its domain.
We know that $\tan^2 x=\frac{\sin^2x}{\cos^2x}$ is defined for all $x\in R$ such that $x\neq \frac{(2n+1)\pi}{2}$, $n$ is integer. Since $\sin x$ and $\cos x$ are continuous then by using the continuity laws, $f(x)=\tan^2 x$ is continuous on its domain.