1. Preview
Warm Up
Lesson Presentation

2. A rocket is fired into the air.
Warm Up
Interpret the graph.
A rocket is fired into the air. y
Rocket ‘s Altitude x
Time
Possible answer: The rocket’s speed increases until gravity gradually slows the rocket and causes it to fall to the ground.

3. Vocabulary
linear equation
linear function

4. Recall that the solution of an equation with one variable is the value of the variable that makes the equation true. The solutions of an equation with two variables are the ordered pairs that make the equation true. When these ordered pairs form a line, the equation is called a linear equation.
A function described by a linear equation is a linear function. To graph a linear function, plot some solutions of the related linear equation, then draw a line through them. The line represents all of the ordered pair solutions of the equation.

5. For example, the function that relates distance d, rate r, and time t is described by the linear equation d = rt. This graph shows solutions of this equation when r = 2 feet per second.
Time (s)
Distance (ft)

6. Additional Example 1: Graphing Linear Functions
Graph the linear function y = 4x – 1.
Make a table.
Input
Rule
Output
Ordered Pair x
4x – 1 y
(x, y)
Substitute positive, negative, and zero values for x.
4(0) – 1 –1
(0, –1) 1
4(1) – 1 3
(1, 3) –1
4(–1) – 1 –5
(–1, –5)

7. Not all linear equations describe functions
Not all linear equations describe functions. The graphs of some linear equations are vertical lines, which do not pass the vertical line test.
Helpful Hint

8. Additional Example 1 Continued
Graph the linear function y = 4x - 1. x y –2 –4 2 4
(1, 3)
Plot each ordered pair on the coordinate grid and then connect the points with a line.
(0, –1)
(–1, –5)

9. Graph the linear function y = 3x + 1.
Check It Out! Example 1
Graph the linear function y = 3x + 1.
Make a table.
Input
Rule
Output
Ordered Pair x
3x + 1 y
(x, y)
Substitute positive, negative, and zero values for x.
3(0) + 1 1
(0, 1) 1
3(1) + 1 4
(1, 4) –1
3(–1) + 1 –2
(–1, –2)

10. Check It Out! Example 1 Continued
Graph the linear function y = 3x + 1. x y
(1, 4) 4
Plot each ordered pair on the coordinate grid. Then connect the points with a line. 2
(0, 1) –4 –2 2 4 –2
(–1, –2) –4

11. Additional Example 2: Earth Science Application
The fastest-moving tectonic plates on Earth move apart at a rate of 15 centimeters per year. Scientists began studying two parts of these plates when they were 30 centimeters apart. Write a linear function that describes the movement of the plates over time. Then make a graph to show the movement over 4 years.
Let x represent the input and y represent the output.
The function is y = 15x + 30, where x is the number of years and y is the total distance apart the two plates are.

12. Additional Example 2 Continued
Input
Rule
Output x
15(x) + 30 y
Multiply the input by 15 and then add 30.
15(0) + 30 30 2
15(2) + 30 60 4
15(4) + 30 90

13. Additional Example 2 Continuedy
100 80 60 40 20 2 4 8 10 12
Graph the ordered pairs (0, 30), (2, 60), and (4, 90) from your table. Connect the points with a line.
Distance (cm) x
Years

14. Graph the linear functions. 1. y = 3x – 4 2. y = –x + 4 3. y = 2
Lesson Review: Part I
Graph the linear functions.
1. y = 3x – 4
2. y = –x + 4
3. y = 2
y = –x +4
y = 2
y = 3x – 4

15. Lesson Review: Part II
4. The temperature of a liquid is decreasing at a rate of 12°F per hour. Susan begins measuring the liquid at 200°F. Write a linear function that describes the change in temperature over time. Then make a graph to show the temperature over 5 hours. y
200
180
160
140
120 1 2 3 4 5
y = 200 – 12x