Unit 1, Lesson 3
Grid Moves
Grade 8
Preparation
Lesson Narrative
Prior to this lesson, students have learned the names for the basic moves (translation, rotation, and reflection) and have learned how to identify them in pictures. In this lesson, they apply translations, rotations, and reflections to figures. They also label the image of a point as . While not essential, this practice helps show the structural relationship (MP7) between a figure and its image.
Students also encounter the isometric grid (one made of equilateral triangles with 6 meeting at each vertex). They perform translations, rotations, and reflections both on a square grid and on an isometric grid. Expect a variety of approaches, mainly making use of tracing paper (MP5) but students may also begin to notice how the structure of the different grids helps draw images resulting from certain moves (MP7).
For classrooms using the digital version of the materials: This is the lesson where students learn to use the transformation tools in GeoGebra.
In this lesson, students review the themes that arose when they shared their initial thoughts in Exercise 1 about what they think it should look like and sound like to do math together as a community. Students then have a chance to both affirm and add to the ideas that were generated.
- Describe (orally) the moves needed to perform a translation, rotation, or reflection.
- Draw and label the image of figures that result from translations, rotations, and reflections on a square or isometric grid.
Let’s transform some figures on grids.
Required Preparation
Make sure students have access to items in their geometry toolkits: tracing paper, graph paper, colored pencils, scissors, ruler, protractor, and an index card to use as a straightedge or to mark right angles.
For classrooms using the print version of the materials: Access to tracing paper is particularly important. Each student will need about 10 small sheets of tracing paper (commercially available "patty paper" is ideal). If using large sheets of tracing paper, such as 8.5 inches by 11 inches, cut each sheet into fourths.
For classrooms using the digital version of the materials: If there is access to extra help from a tech-savvy person, this would be a good day to request their presence in class.
An image is the result of translations, rotations, and reflections on an object. Every part of the original object moves in the same way to match up with a part of the image.
Triangle has been translated up and to the right to make triangle . Triangle is the image of the original triangle .