## Calculus: Early Transcendentals 8th Edition

$x^{2}+1$ for all real numbers $x$.
Start with given expression: $|x^{2}+1|$. Since $x^{2}+1$ must be positive for all $x$, the absolute value is the same as what is inside the absolute value for all $x$: $|x^{2}+1|=x^{2}+1$ for all $x$.