Answer :
We see that the slope of this line is [tex]\frac{-2-1}{2-5}=1,[/tex] so we plug this and the point [tex](5,1)[/tex] into the point-slope form [tex]y-y_1=m(x-x_1)[/tex] (note that there's nothing special about the point I picked; you can choose any point on the line):
[tex]y-1=x-5.[/tex] This rearranges to the slope-intercept form [tex]\boxed{y=x-4}.[/tex]