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Graph a function

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Graph the functiony = xwith domain 0, 2, 4, 6, and 8.

1

2

EXAMPLE 1

Graph a function

SOLUTION

STEP 1

Make an input-output table.

EXAMPLE 1

Graph a function

STEP 2

Plot a point for each ordered pair (x, y).

ANSWER

for Example 1

GUIDED PRACTICE

1. Graph the function y = 2x – 1 with domain 1, 2, 3, 4, and 5.

Years since1997,t

0

1

2

3

4

5

6

Average score, s

511

512

511

514

514

516

519

EXAMPLE 2

Graph a function

SAT Scores

The table shows the average score s on the mathematics section of the Scholastic Aptitude Test (SAT) in the United States from 1997 to 2003 as a function of the time t in years since 1997. In the table, 0 corresponds to the year 1997, 1 corresponds to 1998, and so on. Graph the function.

EXAMPLE 2

Graph a function

SOLUTION

STEP1

Choose a scale. The scale should allow you to plot all the points on a graph that is a reasonable size.

The t-values range from 0 to 6, so label the t-axis from 0 to 6 in increments of 1 unit.

The s-values range from511to519, so label the s-axis from510 to520in increments of2units.

EXAMPLE 2

Graph a function

STEP2

Plot the points.

WHAT IF?In Example 2, suppose that you use a scale on the s-axis from 0 to 520 in increments of 1 unit. Describe the appearance of the graph.

2.

ANSWER

The graph would be very large with all the points near the top of the graph.

EXAMPLE 2

for Example 2

GUIDED PRACTICE

EXAMPLE 3

Write a function rule for a graph

Write a rule for the function represented by the graph.

Identify the domain and the range of the function.

SOLUTION

STEP 1

Make a table for the graph.

EXAMPLE 3

Write a function rule for a graph

STEP 2

Find a relationship between the inputs and the outputs. Notice from the table that each output value is 1 more than the corresponding input value.

STEP 3

Write a function rule that describes the relationship:

y = x+ 1.

ANSWER

A rule for the function is y = x + 1. The domain of the

function is 1, 2, 3, 4, and 5. The range is 2, 3, 4, 5, and 6.

3.

y = 5 – x;domain:0, 1, 2, 3,and4,range: 1, 2, 3, 4,and5

ANSWER

for Example 3

GUIDED PRACTICE

Write a rule for the function represented by the graph. Identify the domain and the range of the function.

ANSWER

y = 5x + 5; domain:1, 2, 3,and4, range: 10, 15, 20, and25

for Example 3

GUIDED PRACTICE

Write a rule for the function represented by the graph. Identify the domain and the range of the function.

4.

EXAMPLE 4

Analyze a graph

Guitar Sales

The graph shows guitar sales (in millions of dollars) for a chain of music stores for the period 1999–2005. Identify the independent variable and the dependent variable. Describe how sales changed over the period and how you would expect sales in 2006 to compare to sales in 2005.

EXAMPLE 4

Analyze a graph

SOLUTION

The independent variable is the number of years since

1999. The dependent variable is the sales (in millions of dollars). The graph shows that sales were increasing. If the trend continued, sales would be greater in 2006 than in 2005.

5.

Based on the graph in Example 4, is $1.4 million a reasonable prediction of the chain’s sales for 2006? Explain.

REASONING

ANSWER

Yes; the graph seems to increase about $0.2 million every two years.

EXAMPLE 4

for Example 4

GUIDED PRACTICE