Using a Protractor

teaching 4th grade how to use a protractor and identify angles

1. Using a Protractor
Geometry Lesson

3. 3
A 180
o
Protractor
Outsidescale from
0
o
to 180
o
going in a
clockwisedirection.
Insidescale from
0
o
to 180
o
going in an
anti-clockwisedirection.

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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 downonto the cross point.
2.Always use the protractor in a horizontal manner as shown
below.


5. Measuring Angles with a Protractor
Place the center point of the protractor on the
vertex of the angle.

6. 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)

7. Measuring Angles with a Protractor
Therefore this angle has a measure of 50°

8. 8
1
2
Measuring
Angles with a
180
o
Protractor
0on the outsideso
use outsidescale
0on the insideso
use insidescale
67
o
50
o

9. 9
3
4
Measuring
Angles with a
180
o
Protractor
0on the outsideso
use outsidescale
0on the insideso
use insidescale
135
o
120
o

10. 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.

11. ACTIVITY 1.
Using a protractor, draw the
following angles with the given
measures.
1. 85°
2. 15°
3. 140°

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REFERENCE:
http://www.mathsrevision.com/index_files/PowerPointLessons.htm

13. ACTIVITY 2.
CLASSIFICATION OF
ANGLES