# What is the domain of sec x?

$\sec x$ is basically nothing more than $\frac{1}{\cos} x$. Therefore, $\sec x$ would simply be undefined wherever $\cos x = 0$. Those points are at $\frac{\pi}{2} \mathmr{and} \frac{3 \pi}{2}$. Therefore, the domain is simply all reals except those two.