take two points from line
[tex]\\ \sf\longmapsto m=\dfrac{y_2-y_1}{x_2-x_1}[/tex]
[tex]\\ \sf\longmapsto m=\dfrac{-1-2}{1-4}[/tex]
[tex]\\ \sf\longmapsto m=\dfrac{-3}{-3}[/tex]
[tex]\\ \sf\longmapsto m=1[/tex]
