Write the equation of a line passing through (–7, 7) and (–6, 9) in slope-intercept form.

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samhouston's profile pic

samhouston | Middle School Teacher | (Level 1) Associate Educator

Posted on

First, calculatge the slope using the slope formula:

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

m = (9 - 7) / (-6 - -7)

m = 2/1

m = 2

Now substitute 2 in for m in the slope-intercept equation.

y = mx + b

y = 2x + b

Now you need to find b, which represents the y-intercept.  Select one of the points and substitute these values in for x and y.

7 = 2(-7) + b

7 = -14 + b

21 = b

You can use the other point to check this.

9 = 2(-6) + b

9 = -12 + b

21 = b

We know the slope is 2 and the y-intercept is 21.

Equation:  y = 2x + 21

Graph the equation and you can see that the line passes through both given points.

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crounds's profile pic

crounds | High School Teacher | (Level 1) eNoter

Posted on

1) find the slope using (y1-y2)/(x1-x2)

2) using either point and the value of the slope, plug them into the slope-intercept equation y = mx + b to find b.

3) rewrite y = mx + b; sub in the slope and y-intercept, here's your equation

(7-9)/-7--6)=m=-2/-1 = 2

7=2(-7)+b   7 = -14 + b   21 = b

y = 2x + 21

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