## Calculus (3rd Edition)

The domain of the function $$f(x)=\sqrt{x^2+9}$$ is $R$ and it is continuous.
Since $x^2+9\geq 0$ for any value of $x\in R$ and is a continuous polynomial, then the domain of the function $$f(x)=\sqrt{x^2+9}$$ is $R$ and it is continuous.