Using a Protractor

Geometry Lesson

3

A 180o Protractor

Outside scale from 0o to 180o going in a clockwise direction.

Inside scale from 0o to 180o going in an

anti-clockwise direction.

21 Apr 2023 4

You need to be able to measure an angle to the nearest degree. To help you do this you should always:1. Look directly down onto the cross point.

2. Always use the protractor in a horizontal manner as shown below.

Measuring Angles with a Protractor Place the center point of the protractor on the

vertex of the angle.

Measuring Angles with a Protractor Read where the top ray crosses the protractor.

(Identifying your angle as acute or obtuse will help you know whether to use the top or bottom set of numbers)

Measuring Angles with a Protractor

Therefore this angle has a measure of 50°

8

1

2

Measuring Angles with a

180o Protractor

0 on the outside so use outside

scale

0 on the inside so use inside scale

67o

50o

9

3

4

Measuring Angles with a

180o Protractor

0 on the outside so use outside

scale

0 on the inside so use inside scale

135o

120o

Drawing Angles with a Protractor

The first step should be to extend the rays that form the angle using a straight edge or a ruler.

ACTIVITY 1.

Using a protractor, draw the following angles with the given measures.

1. 85° 2. 15° 3. 140°