to get the slope of any straight line, we simply need two points off of it, let's use those two points on the picture below.
[tex](\stackrel{x_1}{2}~,~\stackrel{y_1}{4})\qquad (\stackrel{x_2}{2}~,~\stackrel{y_2}{-3}) \\\\\\ \stackrel{slope}{m}\implies \cfrac{\stackrel{rise} {\stackrel{y_2}{-3}-\stackrel{y1}{4}}}{\underset{run} {\underset{x_2}{2}-\underset{x_1}{2}}} \implies \cfrac{-3 -4}{2 -2}\implies \cfrac{-7}{0}\implies und efined[/tex]
