[tex] \bf (\stackrel{x_1}{2}~,~\stackrel{y_1}{5})\qquad
(\stackrel{x_2}{-1}~,~\stackrel{y_2}{5})
\\\\\\
slope = m\implies
\cfrac{\stackrel{rise}{ y_2- y_1}}{\stackrel{run}{ x_2- x_1}}\implies \cfrac{5-5}{-1-2}\implies \cfrac{0}{-3}\implies 0 [/tex]
