[tex]\bf (\stackrel{x_1}{r}~,~\stackrel{y_1}{3})\qquad (\stackrel{x_2}{5}~,~\stackrel{y_2}{-4}) \\\\\\ slope = m\implies \cfrac{\stackrel{rise}{ y_2- y_1}}{\stackrel{run}{ x_2- x_1}}\implies \cfrac{-4-3}{5-r}=\stackrel{\stackrel{slope}{\downarrow }}{-\cfrac{1}{2}}\implies \cfrac{-7}{5-r}=\cfrac{1}{-2} \\\\\\ 14=5-r\implies 9=r[/tex]
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