## Thomas' Calculus 13th Edition

$\{(x,y)\in \mathbb{R}^{2}\ \ |\ \$ $x^{2}+y^{2}\neq 25$ $\}$
There are no restricitions on sine, since it is is defined everywhere. f is defined for points (x,y) that do not yield zero in the denominator. We exclude all points for which $x^{2}+y^{2}=25$ This is a circle about the origin of radius $5$. Since we are excluding it, we graph it with a dashed line. Domain: all points not lying on circle $x^{2}+y^{2}=25$ or, in set notation, $\{(x,y)\in \mathbb{R}^{2}\ \ |\ \$ $x^{2}+y^{2}\neq 25$ $\}$