## Calculus with Applications (10th Edition)

$(-\infty, \infty)$
We want to find all $x$ values for which $f(x)=(x+3)^2$ is defined. We can always add 3 to any real number and then square the result, so the domain of $f$ is all real numbers, which can be expressed in interval notation as $(-\infty, \infty)$.