Question

A line that includes the points (r,7) and (10,3) has a slope of
–4. What is the value of r?

Answer 1

`(\stackrel{x_1}{r}~,~\stackrel{y_1}{7})\qquad (\stackrel{x_2}{10}~,~\stackrel{y_2}{3}) ~\hfill \stackrel{slope}{m}\implies \cfrac{\stackrel{rise} {\stackrel{y_2}{3}-\stackrel{y1}{7}}}{\underset{run} {\underset{x_2}{10}-\underset{x_1}{r}}} ~~ = ~~\stackrel{\stackrel{\textit{\small slope}}{\downarrow }}{-4} \\\\\\ \cfrac{-4}{10-r}=-4\implies -4=-40+4r\implies 36=4r\implies \cfrac{36}{4}=r\implies 9=r`