## Intermediate Algebra (6th Edition)

$y=-1$
Horizontal lines have a slope of $0$. Using $y-y_1=m(x-x_1)$ or the Point-Slope Form, then the equation of the line through $( 3,-1 )$ with slope $0$ is \begin{array}{l} y-(-1)=0(x-3) \\\\ y+1=0 \\\\ y=-1 .\end{array}