Big Ideas Math: Modeling Real Life, Grade 8
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7. Writing Equations in Point-Slope Form
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Exercise 14 Page 183

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

y=3x+2

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. Here, we are given that the line passes through two known points. (-1,-1) and (1,5) To determine the slope of the line, we use the Slope Formula.
m=y_2-y_1/x_2-x_1
m=5-( -1)/1-( -1)
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Simplify right-hand side
m=5+1/1+1
m=6/2
m= 3
Now that we know the slope of the line is 3, 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 ( 1, 5).
y-y_1=m(x-x_1)
y- 5= 3(x- 1)
Since any point on the line could be used to form a point-slope equation, there are infinitely many possible equations. However, we are asked to write the equation in slope-intercept form, so this will give us a unique equation for this line.
y-5=3(x-1)
y-5=(3)x-(3)1
y-5=3x-(3)1
y-5=3x-3
y-5+5=3x-3+5
y=3x+2