# Lesson 9 Use a Protractor to Measure Angles

Let’s use some tools to measure angles.

## Warm-up True or False: There’s Something about 45

Decide if each statement true or false. Be prepared to explain your reasoning.

## Activity 1 How Large is a 1° Angle?

## Problem 1

A ray that turns all the way around its endpoint and back to its starting place has made a full turn or has turned

What fraction of a full turn is each of the following angle measurements?

## Problem 2

Your teacher will give you a **protractor**, a tool for measuring the number of degrees in an angle.

How is

shown on the protractor? How many

measurements do you see?

## Problem 3

A protractor with no numbers has been placed over an angle.

The center of the protractor is lined up with the vertex of the angle.

The straight edge of the protractor is lined up with a ray of the angle.

How many degrees is this angle? Explain how you know.

## Problem 4

An angle contains thirty

## Activity 2 Use a Protractor

## Problem 1

Here are four angles whose sizes you may have estimated earlier. A protractor has been placed over each angle. Measure the size of each angle in degrees.

## Problem 2

Elena and Kiran are measuring an angle with a protractor. Elena says the angle is

## Practice Problem

## Problem 1

Use the given protractor to find the measurement of each angle.