Impossible Graphs
Abstract
This lesson is devoted to impossible graphs. Users of the module can learn
to distinguish between possible and impossible graphs of functions, and to learn why some graphs are impossible.
Objectives
Upon completion of this lesson, students will:
- have practiced
plotting functions on the Cartesian coordinate plane
- be able to read a graph, answering questions about
the situation described by the graph
- be able to look at a graph and decide if it makes
sense
Standards
The activities and discussions in this lesson address the following
NCTM standards:
Algebra
Understand patterns, relations, and functions
- identify functions as linear or nonlinear and contrast their properties from tables, graphs, or equations
Analyze change in various contexts
- use graphs to analyze the nature of changes in quantities in linear relationships
Geometry
Specify locations and describe spatial relationships using coordinate geometry and other representational systems
- use coordinate geometry to represent and examine the properties of geometric shapes
Links to other standards.
Student Prerequisites
- Arithmetic: Students must be able to:
- perform integer and fractional arithmetic
- plot points on the Cartesian coordinate system
- read the coordiates of a point from a graph
- Algebraic: Students must be able to:
- evaluate algebraic expressions in order to
plot points
- Technological Students must be able to:
- perform basic mouse manipulations such as point, click and drag
- use a browser such as Netscape for experimenting with the activities
- use a graphing utility to plot simple algebraic expressions
Teacher Preparation
Students will need:
- Access to a browser
- Copies of supplemental materials for the activities:
Lesson Outline
These activities together give a brief lesson that can be completed
in as little as 30 minutes class-time, depending on how many teams
need to share their ideas. The discovery process takes about 15
minutes, and each presentation about 5 minutes.
- Focus and Review
Remind students what has been learned in previous lessons that will be pertinent to this
lesson and/or have them begin to think about the words and ideas of this lesson:
- Ask the students if they remember how to read graphs.
- Provide them with several graphs and ask them to interpret them.
- Draw a graph on the board for example distance covered in (x)amount of time.
Place a break in the graph making it an impossible graph and ask the students if
they can explain what is "wrong" with it.
- Objectives
Let the students know what it is they will be doing and learning today. Say something
like this:
- Today, class, we are going to learn about impossible graphs and how to determine
if a graph is impossible.
- We are going to use the computers to learn about impossible graphs , but please
do not turn your computers on until I ask you to. I want to show you a little about
this activity first.
- Teacher Input
- Guided Practice
- Next have a "live" discussion while going through the
Possible or not? Activity.
Give each group of students a different graph from the database, and have
them present their ideas and findings to the entire class.
- Independent Practice
- If you choose to pass out the impossible graphs
worksheet have the
students work independantly or in small groups to complete it.
- Closure
- You may wish to bring the class back together for a discussion of the findings.
Once the students have been allowed to share what they found, summarize the results of
the lesson.
Alternate Outlines
This lesson can be rearranged in several ways.
- This lesson can be extended to include not only impossible
graphs, but also non-function graphs (those that do not pass the
vertical line test).
- This lesson can be extended to include having each team of students
discuss a situation in which the impossible graph could be possible.
This is a good place to discuss how time is not the only possible
independent variable.
Suggested Follow-Up
After these discussions and activities, students will have more experience
with functions and relationship between the English description,
graphical and algebraic representations - including what
cannot occur.
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