so, notice in the picture, let's use those points of 0,3 and 1,1
[tex]\bf \begin{array}{ccccccccc}
&&x_1&&y_1&&x_2&&y_2\\
% (a,b)
&&(~ 0 &,& 3~)
% (c,d)
&&(~ 1 &,& 1~)
\end{array}
\\\\\\
% slope = m
slope = m\implies
\cfrac{\stackrel{rise}{ y_2- y_1}}{\stackrel{run}{ x_2- x_1}}\implies \cfrac{1-3}{1-0}\implies \cfrac{-2}{1}\implies -2[/tex]
