## Calculus (3rd Edition)

The domain of $f(x)=\frac{4}{x^4+1}$ is $R$. Also, the range of $f(x)$ is $0\lt y\leq 4$.
Since $x^4+1\neq 0$ for all $x\in R$, then the domain of $f(x)=\frac{4}{x^4+1}$ is $R$. Also, the range of $f(x)$ is $0\lt y\leq 4$.