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The purpose of this activity is for students to identify connections between three different representations of functions: equation, graph, and table. Two of the functions displayed are the same but with different variable names. It is important for students to focus on comparing input-output pairs when deciding how two functions are the same or different.
Give students 1–2 minutes of quiet work time, and follow with a whole-class discussion.
Here are three different ways of representing functions. How are they alike? How are they different?
| -2 | -1 | 0 | 1 | 2 | 3 | |
| 4 | 2 | 0 | -2 | -4 | -6 |
Ask students to share ways the representations are alike and different. Record and display the responses for all to see. To help students clarify their thinking, ask students to reference the equation, graph, or table when appropriate. If the relationship between the inputs and outputs in each representation does not arise, ask students what they notice about this relationship in each representation.
This is the first of three activities in which students make connections between different functions represented in different ways. In this activity, students are given a graph and a table of temperatures from two different cities and are asked to make sense of the representations in order to answer questions about the context (MP2).
Arrange students in groups of 2. Give students 3–5 minutes of quiet work time and then time to share responses with their partner. Follow with a whole-class discussion.
The graph shows the temperature between noon and midnight in City A on a certain day.
The table shows the temperature, , in degrees Fahrenheit for hours after noon in City B.
| 1 | 2 | 3 | 4 | 5 | 6 | |
| 82 | 78 | 75 | 62 | 58 | 59 |
Display the graph and table for all to see. Select groups to share how they used the two different representations to get their answers for each question. To further student thinking about the advantages and disadvantages of each representation, ask:
This is the second of three activities in which students make connections between different functions represented in different ways. In this activity, students are given an equation and a graph of the volumes of two different objects. Students then compare inputs and outputs of both functions and what those values mean in the context of the shapes (MP2).
In the digital version of the activity, students use an applet to compare the two functions. The applet allows students to have an interactive version of the graph to identify coordinates. Use the digital version if it would benefit students identifying points more precisely.
Arrange students in groups of 2. Give students 3–5 minutes of quiet work time and then time to share their responses with their partner. Follow with a whole-class discussion.
As students work, use Collect and Display to create a shared reference that captures students’ developing mathematical language. Collect the language that students use to describe the connections across the two different representations. Display words and phrases, such as “If , then the volume of the cube is 27 cm3 since the equation is ,” “Going up from on the axis, the graph is at a vertical height of about 110 cm3,” “If the input is 2, then on the point on the graph where , I can trace to the left until I reach the vertical axis, where the value of is about 35 cm3,” and “If the input is 2, then in the equation, is equal to 2, so .”
The purpose of this discussion is for students to think about how they used the information from the different representations to answer questions about the context.
Display the equation and graph for all to see. Direct students’ attention to the reference created using Collect and Display. Ask students to share how they used the representations to answer the questions. Invite students to borrow language from the display as needed. As they respond, update the reference to include additional phrases. Consider asking the following questions to prompt students to expand on their answers:
Optional
In this activity, students continue their work comparing properties of functions represented in different ways. Students are given a verbal description and a table to compare and decide whose family traveled farther over the same time intervals. The purpose of this activity is for students to continue building their skill interpreting and comparing functions.
Give students 3–5 minutes of quiet work time, and follow with a whole-class discussion.
Elena’s family is driving on the freeway at 55 miles per hour.
Andre’s family is driving on the same freeway, but not at a constant speed. The table shows how far Andre's family has traveled in miles, , every minute for 10 minutes.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | |
| 0.9 | 1.9 | 3.0 | 4.1 | 5.1 | 6.2 | 6.8 | 7.4 | 8 | 9.1 |
If students do not notice that Elena’s family’s speed has different units than Andre's family, ask
The purpose of this discussion is for students to think about how they use a verbal description and table to answer questions related to the context. Ask students to share their solutions and how they used the equation and graph. Consider asking some of the following questions:
Conclude this lesson by inviting students to summarize some of the strengths and weaknesses of the representations students worked with during the lesson.
Arrange students in groups of 2–3. Give students 3–4 minutes to prepare to answer these question, calling on 1–3 groups for each question:
Functions are all about getting outputs from inputs. For each way of representing a function—equation, graph, table, or verbal description—we can determine the output for a given input.
Let’s say we have a function represented by the equation , where is the dependent variable and is the independent variable. If we wanted to find the output that goes with 2, we could input 2 into the equation for and find the corresponding value of . In this case, when is 2, is 8 since .
If we had a graph of this function instead, then the coordinates of points on the graph would be the input-output pairs.
So we would read the -coordinate of the point on the graph that corresponds to a value of 2 for . Looking at the following graph of a function, we can see the point on it, so the output is 8 when the input is 2.
A table representing this function shows the input-output pairs directly (although only for select inputs).
Again, the table shows that if the input is 2, the output is 8.
| -1 | 0 | 1 | 2 | 3 | |
| -1 | 2 | 5 | 8 | 11 |
The volume, , of a cube with edge length cm is given by the equation .
The volume of a sphere is a function of its radius (in cm), and the graph of this relationship is shown here.
Some students may struggle with the many parts of the second question. These two questions can help scaffold the question for students who need it: