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Big Ideas Math: Modeling Real Life, Grade 8

BI

Big Ideas Math: Modeling Real Life, Grade 8 View details

6. Writing Equations in Slope-Intercept Form

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Exercise 6 Page 175

First, use the given points to calculate the slope. Then, identify the y-intercept.

y=- 3x+2

Practice makes perfect

Equations written in slope-intercept form follow a specific format. y= mx+ b In this form, m is the slope and b is the y-intercept. We need to identify these values using the given graph.

Let's start by substituting the points given on the graph into the Slope Formula and calculating m.

m = y_2-y_1/x_2-x_1

SubstitutePoints

Substitute ( -1,5) & ( 1,-1)

m=-1- 5/1-( -1)

▼

Simplify right-hand side

Subtract term

m=-6/1-(- 1)

a-(- b)=a+b

m=-6/1+1

Add terms

m=-6/2

MoveNegNumToFrac

Put minus sign in front of fraction

m=-6/2

Calculate quotient

m=-3

We calculated that the slope of the given equation is -3. Now, let's calculate the y-intercept and then write the equation in slope-intercepted form.

y-intercept

The y-intercept is the y-value where the line crosses the y-axis.

We can see that the function intercepts the y-axis at (0, 2). This means that the value of b is 2.

Writing the Equation

Now that we have the slope and the y-intercept, we can write our final equation. y= - 3x+ 2

Subchapter links

Try It p.174-175

Self-Assessment for Concepts & Skills p.175

Self-Assessment for Problem Solving p.176

Review & Refresh p.177

Concepts, Skills, & Problem Solving p.177-178