Solve for r

Question

the points (-2,r) (1,6) lie on a line with a slope of -3 find r

Answer 1

 I would like to show you how to find the value of r by using the formula for slope.

 

Slope = (y₂ - y₁) / (x₂ - x₁)

 

Point 1 is (-2, r)

Point 2 is (1, 6)

 

-3 = (6 - r) / (1 - (-2))

-3 = (6 - r) / 3

 

 

Multiply both sides of equation by 3.

 

-9 = 6 - r

 

 

Subtract 6 on both sides of equation.

 

-15 = -r

 

 

Divide both sides of equation by -1 to obtain positive r on one side.

 

15 = r

 

The same solution as Lauren obtained.

Answer 2

So you have the points (-2,r) and (1,6) with a slope of -3. Since slope is simply the change in the y-value / change in x-value for every +1 change in x you have a -3 change in y (or for every -1 change in x you have a +3 change in y as it pertains to this problem). Since the difference between the x values of these points is -3, the change in y is 3*3 or 9 since for every -1 drop in the x value it raises the y value by 3 and the x value drops by -3. So r=6+9=15