The Greedy Triangle
This is a geometry activity based on the picture book The Greedy Triangle.
About this resource
This activity, Polygon Shape up!, is based on the book The Greedy Triangle (words by Marilyn Burns and illustrations by Gordon Silveria).
Specific learning outcomes:
- Create models of several polygons and determine whether they are regular or irregular.
- Use a geometric vocabulary when describing two-dimensional shapes.
The Greedy Triangle
Achievement objectives
GM2-3: Sort objects by their spatial features, with justification.
Description of mathematics
The defining characteristics of two-dimensional shapes are the number of sides and the angles at which the sides meet.
There is a specialised geometry vocabulary to describe two-dimensional shapes.
Required materials
- The Greedy Triangle by Marilyn Burns
- straws, popsticks, or matchsticks
- plasticine, playdough, or Blu-Tack
Activity: Polygon shape up!
A triangle engages the services of the local shape-shifter when he becomes bored. After several visits and gaining angles and sides, he explores the pros and cons of being a quadrilateral and several different polygons. Finally, he happily returns to his life as a triangle, sure that 3 angles and 3 sides is the best thing for him to be.
1.
Prior to reading, explore your students’ understanding of the vocabulary of 2-D shapes. Play Guess My Shape by having a feely bag with several attribute blocks in it. Describe the sides and angles of a shape and have students draw it before you withdraw the shape from the bag. Create a word bank of shape names, especially the common polygons, to refer to when reading the story.
2.
Share the book with your students. Discuss the title and ask them to predict what the triangle will be greedy about. What other shapes can they see on the cover? As you read the story, refer to the words that you already have in the word bank and add any new ones.
3.
After reading, review all the polygon words. Support students in making connections between the root word for a number and the number of sides or angles in the shape. Explain that English often takes root words from other languages. For example, "penta" means 5, and "octa means 8.
4.
Ask students to make several different polygons using the materials provided. Attach the sticks (edges) together with balls of dough. Emphasise that the number of sides and the number of angles (or corners) relate to its name. Explore the idea of “regular” and “irregular” polygons by changing the lengths of the sides being used. A hexagon is any 6-sided shape, but a “regular hexagon” is a 6-sided shape with all sides the same length.
5.
Introduce the shape names in te reo. Ask students to find the pattern within the naming of the shapes.
- Can they predict what a 9-sided or 12-sided polygon is called?
| English | Te Reo |
| triangle | tapatoru |
| rectangle | tapawha |
| pentagon | taparima |
| hexagon | tapaono |
| octagon | tapawaru |
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