Question

(6,2),(9,r),m=-1 find the value of r

Answer 1

The formula of a slope:

$m=\dfrac{y_2-y_1}{x_2-x_1}$

We have the points (6, 2) and (9, r), the slope m = -1. Substitute:

$-1=\dfrac{r-2}{9-6}\\\\-1=\dfrac{r-2}{3}\qquad\text{multiply both sides by 3}\\\\-3=r-2\qquad\text{add 2 to both sides}\\\\\boxed{r=-1}$