# Lesson 8

Sort Triangles

### Lesson Purpose

The purpose of this lesson is for students to classify triangles using angle measures and side lengths.

### Lesson Narrative

The purpose of this lesson is to sort triangles into categories, recognizing right triangles as a category. Students also examine side lengths and notice that sometimes all 3 side lengths are different, sometimes 2 side lengths are equal, and sometimes all 3 side lengths are equal. Students identify right triangles and examine the possible angles that a triangle can have. For example, there are triangles with 3 acute angles but a triangle can only have one right or obtuse angle. Students should have access to straight edges, protractors, and patty paper throughout this lesson.

• Engagement
• MLR7

### Learning Goals

Teacher Facing

• Classify triangles based on angle measurements and side lengths.

### Student Facing

• Let’s sort triangles.

### Required Materials

Materials to Copy

• Card Sort Triangles (Grade 5)

### Required Preparation

Activity 1:

• Create a set of cards from the blackline master for each group of 2.

Activity 2:

• Gather materials from previous activity:
• Triangle Cards

### Lesson Timeline

 Warm-up 10 min Activity 1 20 min Activity 2 15 min Lesson Synthesis 10 min Cool-down 5 min

### Teacher Reflection Questions

How are students applying what they learned about the hierarchy of quadrilaterals to help them make sense of classifying triangles?