1. Warm Up
Problem of the Day
Lesson Presentation
Lesson Quizzes

2. Warm Up
Evaluate each equation for x = –1, 0, and 1.
1. y = 3x
2. y = x – 7
3. y = 2x + 5
4. y = 6x – 2
–3, 0, 3
–8, –7, –6
3, 5, 7
–8, –2, 4

3. Write a linear equation that contains terms with x2.
Problem of the Day
Write a linear equation that contains terms with x2.
Possible answer: x2 + y = x2 + x + 4

4. Sunshine State Standards
MA.8.A.1.2 Interpret the slope…when graphing a linear equation for a real-world problem.
Also MA.8.A.1.1

5. Vocabulary
rise
run
slope 5

6. The constant rate of change of a line is called the slope of the line.

7. Additional Example 1: Finding the Slope of a Line
Find the slope of the line.
Begin at one point and count vertically to find the rise.
Then count horizontally to the second point to find the run.
slope = = 3 6 1 2
The slope of the line is . 1 2

8. Check It Out: Example 1
Find the slope of the line.
Use points (0, –1) and (1, 1).
2 1
slope = = 2

9. If you know any two points on a line, or two solutions of a linear equation, you can find the slope of the line without graphing. The slope m of a line through the points (x1, y1) and (x2, y2) is as follows:
y2 – y1
x2 – x1
m =

10. Additional Example 2: Finding Slope, Given Two Points
Find the slope of the line that passes through (–2, –3) and (4, 6).
Let (x1, y1) be (–2, –3) and (x2, y2) be (4, 6). =
y2 – y1
x2 – x1
6 – (–3)
4 – (–2)
Substitute 6 for y2, –3 for y1,
4 for x2, and –2 for x1. 9 6 = 3 2 =
The slope of the line that passes through (–2, –3) and (4, 6) is . 3 2

11. Check It Out: Example 2
Find the slope of the line that passes through (–4, –6) and (2, 3). =
–6 – 3
–4 – 2 –9 –6 3 2 = =
3–(–6)
2–(–4) 9 6 3 2 = or

12. Additional Example 3: Money Application
The table shows the total cost of fruit per pound purchased at the grocery store. Use the data to make a graph. Find the slope of the line and explain what it shows.
Pounds
Cost
Cost of Fruit
Graph the data.

13. Additional Example 3 Continued
Find the slope of the line: =
y2 – y1
x2 – x1
30 – 15
10 – 5 15 5 =
= 3
The slope of the line is 3. This means that for every pound of fruit, you will pay another $3.

14. Check It Out: Example 3
The table shows how much money Andre and Marla made working at the concession stand at a baseball game one weekend. Use the data to make a graph. Find the slope of the line and explain what it shows.
Time Worked (h)
Amount Earned($) 2 15 4 30 6 45 8 60

15. Check It Out: Example 3 Continued
Find the slope of the line: 15 2 =
30 – 15
4 – 2
or 7.5
slope =
This means that they earn $7.50 per hour.

16. The slope of a line my be positive, negative, zero, or undefined.

18. Lesson Quiz for Student Response Systems
Lesson Quizzes
Standard Lesson Quiz
Lesson Quiz for Student Response Systems 18 18

19. Lesson Quiz: Part I
Find the slope of the line passing through each pair of points.
1. (4, 3) and (–1, 1)
2. (–1, 5) and (4, 2) 2 5 5 3 –

20. Lesson Quiz: Part II
3. The table shows how much money Susan earned as a house painter for one afternoon. Use the data to make a graph. Find the slope of the line and explain what it shows.
The slope of the line is 7. This means Susan earned $7 for each hour worked. x y 6 4 2 8 10 12 14 20 30 40 50 60 70 80

21. Lesson Quiz for Student Response Systems
1. Identify the slope of the line passing through the pair of points (5, 2) and (–2, 1).
A. 7
B. –3 C. D. 21 21

22. Lesson Quiz for Student Response Systems
2. The table shows the number of hours a student works and her earnings. Identify the slope of the line and explain what it shows.
A. The slope of the line is 15. This means that the student earns $15 for every hour that she works.
B. The slope of the line is 30. This means that the student earns $30 for every hour that she works. 22 22