# Lesson 10

Angle Measurement and Perpendicular Lines

### Lesson Purpose

**perpendicular lines**.

### Lesson Narrative

In a previous lesson, students learned that a 1-degree angle measures a turn through \(\frac{1}{360}\) of a circle and that a protractor could be used to measure angles in degrees.

In this lesson, students practice using a protractor to measure a variety of angles—angles formed by rays or line segments and those that are in other two-dimensional figures. Students consider how to position the tool, which set of numbers to use, and whether their measurements make sense.

Next, students are prompted to fold paper to create two lines that form right angles. They learn that intersecting lines that form \(90^\circ\) angles are **perpendicular**. They then practice identifying perpendicular lines and segments.

- Representation

- MLR8

### Learning Goals

Teacher Facing

- Recognize that perpendicular lines meet or cross at a right angle.
- Use a protractor to measure angles.

### Student Facing

- Let’s measure all kinds of angles.

### Required Materials

Materials to Gather

### Required Preparation

Activity 2:

- Prepare at least 2 pieces of paper (or sticky notes) for each student.

### Lesson Timeline

Warm-up | 10 min |

Activity 1 | 15 min |

Activity 2 | 20 min |

Lesson Synthesis | 10 min |

Cool-down | 5 min |

### Teacher Reflection Questions

### Suggested Centers

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