First use the slope formula:

where (x1,y1) = (-9,7)
and where (x2,y2) = (9,-1)









Now that you have the slope, use the point-slope formula:



where (x1,y1) = (-9,7)

[Don't substitute anything for variables x and y, but leave them
as they are and just substitute for x1 and y1.]







That's the slope y-intercept form.  If
you like you can get it into general form.
Multiply through by 9 to clear the fraction:





Edwin