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Using a Protractor
Geometry Lesson
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.
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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.

23-May-17
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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°
1
Measuring
Angles with a
180o Protractor
50o
2
0 on the inside so
use inside scale
67o
0 on the outside so
8
use outside scale
3
Measuring
Angles with a
180o Protractor
120o
4
135o
0 on the outside so
9
use outside scale
0 on the inside so
use inside scale
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°