Question

The points (-1, -3) and (2, r) lie on a line with slope 3. Find the missing coordinate r.

Answer 1

r=6

Explanation:

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

r+3/3 = 3/1

cross-multiply:

r+3 = 9

r = 6

Check:

6-(-3)/2-(-1) should equal 3

9/3 = 3

checks out correctly

Answer 2

r = 6

Explanation:

Formula

m = (y2 - y1)/(x2 - x1)

Givens

x1 = - 1

x2 = 2

y1 = - 3

y2 = r

m = 3

Solution

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

3 = (r + 3) / 3 Multiply both sides by 3

9 = r + 3 Subtract 3 from both sides

6 = r + 3 - 3

6 = r