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Slope of a Line
Warm Up
Lesson Presentation
Problem of the Day
Lesson Quizzes
Slope of a Line
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
Slope of a Line
Problem of the Day
Write a linear equation that contains terms with x2.
Possible answer: x2 + y = x2 + x + 4
Slope of a Line
Learn to find the slope of a line and use
slope to understand and draw graphs.
Slope of a Line
Vocabulary
rise
run
slope
Slope of a Line
The constant rate of change of a line is called the slope of the line.
Slope of a Line
(5, 4)
(1, 2) Then count horizontally to the second point to find the run.
Find the slope of the line.
Begin at one point and count vertically to find the rise.
Additional Example 1: Finding the Slope of a Line
slope = = 2 4
1 2
The slope of the line is . 1 2
Slope of a Line
(3, 2)
(–1, –2)
Then count horizontally to the second point to find the run.
Find the slope of the line.
Begin at one point and count vertically to find the rise.
Check It Out: Example 1
slope = = 1 4 4
The slope of the line is 1.
Slope of a Line
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 =
Slope of a Line
Find the slope of the line that passes through (–2, –3) and (4, 6).
Additional Example 2: Finding Slope, Given Two
Points
Let (x1, y1) be (–2, –3) and (x2, y2) be (4, 6).
6 – (–3) 4 – (–2)
Substitute 6 for y2, –3 for y1, 4 for x2, and –2 for x1.
9 6
=
The slope of the line that passes through
(–2, –3) and (4, 6) is . 3 2
= y2 – y1 x2 – x1
3 2
=
Slope of a Line
Find the slope of the line that passes through (–4, –6) and (2, 3).
Check It Out: Example 2
Let (x1, y1) be (–4, –6) and (x2, y2) be (2, 3).
3 – (–6) 2 – (–4)
Substitute 3 for y2, –6 for y1, 2 for x2, and –4 for x1.
9 6
=
The slope of the line that passes through
(–4, –6) and (2, 3) is . 3 2
= y2 – y1 x2 – x1
3 2
=
Slope of a Line
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.
Graph the data.
Pounds
Co
st
Cost of Fruit
Slope of a Line
Additional Example 3 Continued
Find the slope of the line:
The slope of the line is 3. This means that for every pound of fruit, you will pay another $3.
= y2 – y1 x2 – x1
15 5
=
30 – 15 10 – 5
= 3
Slope of a Line
Check It Out: Example 3
The table shows the total cost of gas per gallon. Use the data to make a graph. Find the slope of the line and explain what it shows.
Graph the data.
Cost of Gas
Gallons Cost
0 0
3 6
6 12
6
9
9
12
6 0
3
3 x
y
Gallons
Cost of Gas
Co
st
Slope of a Line
Check It Out: Example 3 Continued
Find the slope of the line:
The slope of the line is 2. This means that for every gallon of gas, you will pay another $2.
= y2 – y1 x2 – x1
6 3
=
12 – 6 6 – 3
= 2
Slope of a Line
Slope of a Line
Slope of a Line
Standard Lesson Quiz
Lesson Quizzes
Lesson Quiz for Student Response Systems
Slope of a Line
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 –
Slope of a Line
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.
x
y
6 4 2 8 10 12 14 0
10
20
30
40
50
60
70
80
The slope of the line is 7. This means Susan earned $7 for each hour worked.
Slope of a Line
1. Identify the slope of the line passing through the pair of points (5, 2) and (–2, 1). A. 7 B. –3 C. D.
Lesson Quiz for Student Response Systems
Slope of a Line
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.
Lesson Quiz for Student Response Systems