Chapter 3 - Introduction to Graphing - 3.7 Point-Slope Form and Equations of Lines - 3.7 Exercise Set - Page 218: 37

$y=-1(x-9)$

Using $y-y_1=m(x-x_1)$ or the Point-Slope form where $m$ is the slope and $(x_1,y_1)$ is a point on the line, then the equation of the line with the given slope equal to $ -1 $ and with the given point $\left( 9,0 \right)$ is \begin{array}{l} y=-1(x-9) .\end{array}