The point-slope form:
[tex]y-y_1=m(x-x_1)\\\\m=\dfrac{y_2-y_1}{x_2-x_1}[/tex]
We have two points (-9, 7) and (9, 1). Substitute:
[tex]m=\dfrac{1-7}{9-(-9)}=\dfrac{-6}{18}=-\dfrac{1}{3}\\\\y-7=-\dfrac{1}{3}(x-(-9))\\\\\boxed{y-7=-\dfrac{1}{3}(x+9)}[/tex]
