## College Algebra 7th Edition

$y=5$
RECALL: (1) Perpendicular lines have slopes whose product is $-1$ (or negative reciprocal slopes). (2) A horizontal line has a slope of $0$ and has an equation of the form $y=k$ where $k$ is the y-coordinate of all the points on the line. (4) Horizontal lines are parallel to each other. The line is parallel to the x-axis. Since the axis is a horizontal line, its slope is $0$. This means that the slope of the line we are looking for is also $0$. The horizontal line we are looking for the equation of passes through $(4, 5)$. The y-coordinate of this point is $5$. Therefore, the equation of the line we are looking for is $y=5$.