# 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.

## 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.

1. How is shown on the protractor?

2. 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 angles, as shown. How many degrees is this angle?

## 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 . Kiran says it shows . Why might they end up with different measurements? Which one is correct? Explain your reasoning.

## Problem 1

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