# Lesson 12

Types of Angles

### Lesson Purpose

The purpose of this lesson is for students to classify angles as acute, obtuse, and straight, and to identify and draw acute and obtuse angles.

### Lesson Narrative

In previous lessons, students learned to measure angles and draw angles of given measurements. They saw that a $$90^\circ$$ angle is called a right angle and is formed by two perpendicular lines. Students are also familiar with some benchmark angle measurements.

In this lesson, students classify angles by their size and identify angles as acute or obtuse in a variety of contexts. Students also learn that a $$180^\circ$$ is called a straight angle.

• Representation

### Learning Goals

Teacher Facing

• Draw acute and obtuse angles.
• Identify acute, obtuse, right, and straight angles in two-dimensional figures.

### Student Facing

• Let’s look at different types of angles.

### Required Materials

Materials to Gather

### Required Preparation

Activity 1:

• Students need their angle cards from the previous lesson.

Building On

### Lesson Timeline

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

### Teacher Reflection Questions

Before this point, students have had experiences of sorting mathematical objects relative to some benchmarks. In this lesson, angles are categorized by their size and relative to two benchmarks: $$90^\circ$$ and $$180^\circ$$. How readily did students conceptualize angles this way? Which past experiences of classifying objects would help to make this idea more intuitive?

### Suggested Centers

• Which One? (K–5), Stage 4: Grade 3 Shapes (Supporting)
• Can You Draw It? (1–5), Stage 4: Area and Perimeter (Supporting)