keeping in mind that perpendicular lines have negative reciprocal slopes, let's check for the slope of the equation that goes through (5,4) and (10,2)
[tex](\stackrel{x_1}{5}~,~\stackrel{y_1}{4})\qquad (\stackrel{x_2}{10}~,~\stackrel{y_2}{2}) ~\hfill \stackrel{slope}{m}\implies \cfrac{\stackrel{rise} {\stackrel{y_2}{2}-\stackrel{y1}{4}}}{\underset{run} {\underset{x_2}{10}-\underset{x_1}{5}}}\implies \cfrac{-2}{5} \\\\[-0.35em] ~\dotfill[/tex]
[tex]\stackrel{\textit{perpendicular lines have \underline{negative reciprocal} slopes}} {\stackrel{slope}{-\cfrac{2}{5}}\qquad \qquad \qquad \stackrel{reciprocal}{-\cfrac{5}{2}}\qquad \stackrel{negative~reciprocal}{+\cfrac{5}{2}\implies \cfrac{5}{2}}}[/tex]
