Lesson 4

Building with Triangles

Est. Class Sessions: 2
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Mathematical Standards

3.G.A
Reason with shapes and their attributes. (3.G.A.1)

Standards for Mathematical Practice

MP1.
Make sense of problems and persevere in solving them.
MP2.
Reason quantitatively.
MP5.
Use appropriate tools strategically.
MP7.
Look for and make sense of structure.

Students make shapes by putting two or three isosceles right triangles together edge to edge. For each shape, they determine the number of sides, vertices, right angles, and lines of symmetry.

Content in this Lesson

  • Analyzing and classifying shapes using their properties (number of sides, vertices, and right angles) [E1].
  • Identifying shapes that are congruent [E5].
  • Identifying lines of symmetry [E6].
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Materials for Students

Daily Practice and Problems Lesson Homework Assessment

Student Books

 Student Guide
Student Activity Book

Teacher Resources

 Teacher Guide - digital

Supplies for Students

ruler
scissors
crayons or colored pencils
drawing paper, optional

Supplies for Student Pairs

4 small triangles from 2 tangram sets or cut from card-stock copies of Right Triangle Master (Teacher Guide)
envelope for storing triangles
square from a tangram set, optional

Materials for the Teacher

Display of Lines of Symmetry Master (Teacher Guide)
Display of When Are Shapes the Same? page (Student Activity Book) Page 433
Display of 4 small triangles from the Right Triangle Master (Teacher Guide)
Display of Building with Two Triangles page (Student Activity Book) Page 435
Unit 11 Assessment Record
two display sets of tangram pieces
chart paper

Materials Preparation

Prepare the Master. Prepare a copy of the When Are Shapes the Same? page in the Student Activity Book for display. Cut out Triangle Z and Shape Y at the bottom of the page. Color both sides of each shape.

Prepare Right Triangles. For this lesson, each student pair needs four isosceles right triangles of the size shown in Figure 1. The smallest triangles in a set of tangrams are this size. If tangrams are not available, a copy of the Right Triangle Master will provide enough triangles for twelve pairs of students. If possible, make the copies on a sturdy material like card stock. Students should store their triangles in envelopes.

Figure 1
Figure 1: Student pairs need four triangles of this size and shape to complete this lesson

Assessment in this Lesson

Assessment Expectation Assessed

Investigating Shapes
with Feedback Box
Teacher Guide - digital
E1.
Describe and analyze two-dimensional shapes using their properties (e.g., number of sides, length of sides, vertices, number and size of angles, number of right angles, and relationships between sides).
E5.
Identify congruent shapes.
E6.
Identify lines of symmetry.