# In this Geometer’s Sketchpad lesson, similar polygons and a table of data to show the relationships between the figures are constructed

Subject:

Math

7

Title – Similar Polygons using Geometer’s Sketchpad
By – Rachel Hutcherson
Primary Subject – Math

Content:

Students will use Geometer’s Sketchpad to construct varying types of similar polygons. They will measure the sides and the angles and then form a table of data to show the relationships between the figures.

Benchmarks:

G.TR.07.03:

• Understand that in similar polygons, corresponding angles are congruent and the ratios of corresponding sides are equal
• Understand the concepts of similar figures and scale factor

Learning Resources and Materials:

• Computer
• Worksheet containing pictures of different polygons (teacher created)

Development of Lesson:

Introduction:

• This lesson can be easily related to past experiences, because it involves using students’ previous knowledge of angles, segments, and measuring to complete.
• Also, they will know the definitions of corresponding angles, congruent, similar figures, and corresponding sides.
• Students will have had previous experience in working with Geometer’s Sketchpad, so the program will not be foreign to them.
• Students will be prepared for this lesson by reviewing the properties of polygons. They will know that a quadrilateral has four sides and four angles, the measure of which adds up to 360 degrees; a pentagon has five sides and five angles that add up to 540 degrees, and so on. They will also be provided with a worksheet that has this information on it for a reference.
• To get students to focus on the task at hand, inform them on what is going to take place before they get to the computers. This way they are not distracted by the computers while receiving instructions and other information.

Methods/Procedures:

All of the students will be working individually and will have the freedom to change the color of their polygons, font, and tables. Instructions will be given at the beginning of class, and will also be posted on the board as a reference for the students.
1. The students need to open the Geometer’s Sketchpad program. Each student will be given three different regular polygon figures to work with which they will have to identify.
2. Next they will click on each side of the polygons and then click on the “Measure” tool (they will be measuring length).
3. Then, the students will measure each angle of each polygon by clicking on three vertices at a time and going to the “Measure” menu (click on “Angle”).
4. After taking each of the polygon’s measurements, the students will form a table for their data. To do this they need to select each measurement, go to the “Graph” menu, and select “Tabulate.”
5. To get more data, the students will add a new row to their tables by double clicking on the last row. Then they will drag the three polygons by using the vertices. The new measures will show up in the table. Students will need at least four rows of data.
6. Once the data table has been developed, students will be able to see the similarities between the lengths of sides and the angles of each polygon.

After the students have completed the procedures, ask questions such as what they noticing about the lengths of the sides of the similar polygons, and whether the angles are the same or not. Leave the questions open for discussion.

Accommodations and adaptations can easily be made to this assignment. For example, students with different learning levels could work together. Also the lesson could be shortened or lengthened by either adding or removing polygon shapes, or by providing some of the measurements.

Assessment/Evaluation:

To check for understanding, the students’ work will be reviewed and questions will be asked. Feedback should be given throughout the lesson so students know whether they are on the right track or not. As a final assessment, students should write a paragraph or two on their findings, which should be able to show whether learning took place and whether each student met the benchmark or not.

Closure:

At the end of the lecture, the class will discuss their findings with one another. The teacher and students should discuss what properties similar polygons have and why they are considered similar and not congruent. Also it would be a good idea to discuss any problems that the students had with the Geometer’s Sketchpad program, and whether anything could be done differently.

Teacher Reflection:

The teacher should reflect on what the students did during the lesson as well as the questions and answers they came up with during the class discussion. Then he or she should reflect on if anything could be done better.

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