# Lesson 5

What is an Angle?

### Lesson Purpose

The purpose of this lesson is to introduce angles and to motivate a need for vocabulary to describe what they are and their size.

### Lesson Narrative

In this lesson, students are introduced to angles. They learn that an angle can be defined in terms of the geometric parts they have been working with in this unit.

In previous grades, students have used “square corners” to describe right angles within two-dimensional shapes. They may have considered an angle as the space within a square corner or the “pointy” corner itself. Here, students learn that an angle is a geometric figure made up of two rays that share the same endpoint, which we refer to as the vertex of the angle.

Throughout the lesson, students use the vocabulary they have developed to describe other geometric figures to identify and describe angles. Monitor for the ways students reason about how to describe the size of angles. Students will compare and measure angles in future lessons.

• Engagement

### Learning Goals

Teacher Facing

• Identify angles in two-dimensional figures.
• Recognize angles as geometric figures that are formed wherever two rays share a common endpoint.

### Student Facing

• Let’s look for angles and find out ways to describe them.

### Required Materials

Materials to Gather

Materials to Copy

• Tricky Figures

### Required Preparation

Activity 1:

• Create a set of cards (4 cards total) for each group of 2 from the blackline master.
• Each group of 2 needs 2 cards (sets 1 and 2). Additional cards (sets 3A and 3B) can be used for extension.

Building Towards

### Lesson Timeline

 Warm-up 5 min Activity 1 15 min Activity 2 15 min Activity 3 10 min Lesson Synthesis 10 min Cool-down 5 min

### Teacher Reflection Questions

What was the best question you asked students today? Why would you consider it the best one based on what students said or did?

### Suggested Centers

• Target Measurements (2–5), Stage 4: Degrees (Addressing)
• Compare (1–5), Stage 5: Fractions (Supporting)