Page 12 - Key Stage 3 Geometry
P. 12
2 Angles and the Protractor
Whenever two lines cross,
angles subtend between them
as shown in the diagram on the
left. Angles are measured in
degrees which is indicated by a
o , each angle is subdivided into 60 minutes, indicated
by a ’ and each minute is subdivided into 60 seconds
(or arcseconds) indicated by a ”. In the above diagram
o
all the angles add up to 360 , what you would find in
a full circle. Therefore,
+ + + = 360
or
2 + 2 = 2( + ) = 360
Dividing both sides by 2
+ = 180
Angles fall into four categories, as shown below.
Acute angle Right angle
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