Big Ideas Math: Modeling Real Life, Grade 8
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7. Writing Equations in Point-Slope Form
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Exercise 9 Page 181

Point-slope form is y-y_1=m(x-x_1).

Example Solution: y-1=-3/2(x-3)

Practice makes perfect
Equations in point-slope form follow a specific format. y- y_1= m(x- x_1) In this form, m is the slope of the line and ( x_1, y_1) is a point on the line. Let's choose two points from the given table. (3,1) and (7,-5) To determine the slope of the line, we use the Slope Formula.
m=y_2-y_1/x_2-x_1
m=-5- 1/7- 3
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Simplify right-hand side
m=-6/4
m=-6/4
m=-6/2/4/2
m=-3/2
Now that we know the slope of the line is - 32, we can write the equation of the line in point-slope form. We can use either of the given points as (x_1,y_1) in our equation. Let's use ( 3, 1).
y-y_1=m(x-x_1)
y- 1= -3/2(x- 3)
Please note that any point on the line can be used to form a point-slope equation. Therefore, our equation is only one of infinitely many possible equations!