Chapter 3 - Introduction to Graphing - 3.3 Graphing and Intercepts - 3.3 Exercise Set - Page 180: 93

$y=0$

RECALL: (1) For the point $(x, y)$, the y-coordinate represents the distance of the point from the x-axis. (2) The equation of a horizontal line is $y=k$ where $k$ is a real number. The x-axis is a horizontal line. All points on the x-axis are 0 units away from the x-axis, so their y-coordinate is $0$. Thus, the equation of the x-axis is $y=0$.