Page 109 - Math Course 3 (Book 1)

Writing Linear Equations

Write an Equation to Make a Prediction
Step 3 Write the equation. WEATHER
Attendance at an outdoor sporting event is
y = mx + b Slope-intercept form
affected by the temperature outside. When the
outside temperature is 0°F, the attendance is 12
y = –6x + 150 Replace m with –6 and b people. For every increase in temperature of 20
with 150.
degrees, the attendance increases by 100 people.
Step 4 Substitute the distance of 20 miles. Predict the attendance if the temperature is 60°F.

y = –6x + 150 Write the equation. A. 112
B. 300
y = –6(20) + 150 Replace x with 20. C. 312
D. 412
y = 30 Simplify.
Answer
At a distance of 20 miles, the
Answer
number of customers is 30.

Your Turn!

Write Equations From Slope and y-Intercept
Write an equation in slope-intercept form for the MO. 3 - L7b
line. slope = –3, y-intercept = –5
Writing Equations:
A. y = –3x + 5
B. 3x + y = –5 Graph, Table, or Two Points
C. y = –5x – 3
D. y = –3x – 5
Let’s Begin

Answer
Write an Equation From a Graph

Examples

Write an equation in slope-intercept form for the
line graphed.
Write an equation in slope-intercept form for the
line. slope = 0, y-intercept = 9

A. y = x + 9
B. y = 9
C. y = –9
D. y = 9x

Answer
The y-intercept is –4. From (0, –4), you can go up
one unit and to the right one unit to another point
on the line. So, the slope is 1.

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