Lesson 9

Describing and Analyzing Shapes

Est. Class Sessions: 1–2

Developing the Lesson

Part 1. Use Properties to Play Shape Finder

Introduce Shape Finder. Begin the lesson by playing Shape Finder with Power Polygons™. Give each pair of students 2 sets of Power Polygons™ and ask them to have scratch paper and a pencil ready.

Display the Shape Finder Chart you prepared and tell students the rules of the game:

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  • I will name a property of a shape. A property is an attribute or characteristic of a shape that helps you identify it. For example, I might say, “Find a shape with four sides.” Or, “Find a shape with a right angle.”
  • Be ready to show or tell how you made your choice.

Figure 3 shows the Power Polygons™ labeled with letters. Use the figure to check students' responses.

Have students work in pairs to find at least one shape that has each property and to prepare explanations for their choices. Encourage students to use sides and angles of other shapes for comparison. They can also trace the shapes, so that they can rotate or fold them as part of their explanations.

For each property, have volunteers demonstrate for the class how they know their shapes have that property. The table in Figure 4 provides a list of properties, examples of shapes, and lists one possible explanation for identifying each property. Others are possible. It is not necessary for the class to find every shape that has a given property. However, continue the discussion long enough to find different shapes with the same property. For example, all of the following shapes in the Power Polygons™ set have the property all angles are equal: the rectangle (C), square (A, B), hexagon (H), and equilateral triangles (I, N).

As the class discusses each property, build a Shape Finder chart of the properties with two or three examples of the shapes sketched or traced on the chart. This will compile a record of the properties and corresponding shapes that students can use in the remaining lessons of the unit. See Figure 5 for the beginning of a sample chart.

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At this point in students' development, it is not necessary for them to give a rigorous geometric proof to justify their choices of shapes. For example, they do not yet have the tools to prove that opposite sides of a given shape are parallel. It is enough for them to visually identify the parallel sides and show that they understand what it means for lines to be parallel. However, they should be clear in their explanations and be able to point to the parts of the shapes they discuss.

Describe Sides and Angles. After you have completed the Shape Finder game, introduce students to the terms “opposite sides” and “opposite angles.” This activity will help develop language for describing and analyzing shapes.

Have students touch the appropriate parts of the polygons as you ask:

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  • Find the large green rhombus (Shape G). Touch the sides that are opposite. What can you tell me about the opposite sides of this figure? (Both pairs of opposite sides appear to be parallel. Both pairs of opposite sides are also the same length.)
  • Which sides meet at a vertex (corner)? (The sides that are next to each other, not the opposite sides.)
  • Touch the angles that are opposite each other. What can you say about the size of the opposite angles? (Both pairs of the opposite angles in the green rhombus are the same size.)
  • Now find the blue rectangle (Shape C). What can you say about the opposite sides of this rectangle? (Both pairs of opposite sides appear to be parallel and are also the same length.)
  • What can you say about the sides that meet? (They are perpendicular and form a right angle.)
Student Guide:
Student Activity Book:
Master:
Power Polygons™ labeled with letters
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A list of properties with sample shapes and possible student explanations for the Shape Finder chart
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Sample Shape Finder chart of properties and example shapes
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