Question

The points (-2,9) and (2,r) lie on a line with slope -3. Find the missing coordinate r

Answer 1

The formula of a slope:

`m=(y_2-y_1)/(x_2-x_1)`

We have the points (-2, 9) and (2, r) and the slope m = -3. Substitute:

`(r-9)/(2-(-2))=-3\\\\(r-9)/(2+2)=-3\\\\(r-9)/(4)=-3\qquad\text{multiply both sides by 4}\\\\r-9=-12\qquad\text{add 9 to both sides}\\\\\boxed{r=-3}`