The points (7,r) and (12,6) lie on a line with slope 3. Find the missing coordinate r.

Question

I need help with algebra 1

Answer 1

The slope = 3

The two points on the line are (7,r) and (12,6).

Let (7,r) be (x1,y1) and (12,6) be (x2,y2)

slope = (y2-y1)/(x2-x1) = 3

(6-r)/(12-7)=3

(6-r)/5 = 3

cross multiply

6-r = 15

6-15 = r

r= -9

Answer 2

The slope (incline, grade, slant, tilt, ...) of a line is sometimes called "rise over run."

In the slope-intercept form of the equation of a line, y = mx+b, the slope is m.

m = (y₂-y₁) / (x₂-x₁)

In this problem, the y-coordinate of the first point, given as r, must make the slope equal to 3.

m = (6-r) / (12-7) = 3

(6-r) / 5 = 3

6-r = 15

-r = 9

r = -9