Answer
domain: $\mathbb{R}$
interval notation: $(-\infty,\infty)$
Work Step by Step
See example 1.
Division by 0 is undefined, so
$f(x)$ will be defined for all real numbers except for
the number(s) x that yield zero in the denominator:
$x^{2}+49=0$
$x^{2}=-49$
... no real number has a negative square...
... so, the denominator is never zero,
$f$ is defined for all real numbers
domain: $\mathbb{R}$
interval notation: $(-\infty,\infty)$
