Big Ideas Math: Modeling Real Life, Grade 8
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Big Ideas Math: Modeling Real Life, Grade 8 View details
7. Writing Equations in Point-Slope Form
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Exercise 1 Page 183

Start by using the Slope Formula to find the slope.

y=1/2x+5

Practice makes perfect
An equation in slope-intercept form follows a specific format. y= mx+ b For an equation in this form, m is the slope and b is the y-intercept. We can calculate the slope by substituting two points from the given table into the Slope Formula. Let's choose the points (-2,4) and (0,5).
m = y_2-y_1/x_2-x_1
m=5- 4/0-( -2)
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Simplify right-hand side
m=5-4/0+2
m=1/2
A slope of 12 means that for every 2 horizontal steps in the positive direction, we take 1 vertical step in the negative direction. Now that we know the slope, we can write a partial version of the equation. y= 1/2 x+ b To complete the equation, we also need to determine the y-intercept b. Since we know that the given points will satisfy the equation, we can substitute one of them into the equation to solve for b. Let's use ( 0, 5).
y=1/2x+b
5=1/2( 0)+b
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Solve for b
5=0+b
5=b
b=5
A y-intercept of 5 means that the line crosses the y-axis at the point (0, 5). We can now complete the equation. y= 1/2x+ 5