Angle

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Angle Measurements
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Degrees Measuring Angles
We measure the size of an angle using degrees.
Example Here are some examples of angles and
their degree measurements.
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Protractor
A device used to measure angles.
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Acute Angles An acute angle is an angle
measuring between 0 and 90 degrees. Example
                                                 
              
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Obtuse Angles An obtuse angle is an angle
measuring between 90 and 180 degrees. Example
                                                 
                
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Right Angles A right angle is an angle measuring
90 degrees. Examples                      
                 
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Complementary Angles Two angles are called
complementary angles if the sum of their degree
measurements equals 90 degrees. Example
These two angles are complementary.
                                                  
                             
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These two angles can be "pasted" together to form
a right angle!                         
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Supplementary Angles Two angles are called
supplementary angles if the sum of their degree
measurements equals 180 degrees. Example
These two angles are supplementary.
                                                  
                    
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These two angles can be "pasted" together to form
a straight line!                               
                  
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Vertical Angles For any two lines that meet,
such as in the diagram below, angle AEB and
angle DEC are called vertical angles. Angle BEC
and angle AED are also vertical angles. Vertical
angles have the same degree measurement.
                                   
110
70
70
110
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Review
State whether the following are acute, right, or
obtuse.
1.
3.
5.
acute
obtuse
right
2.
4.
?
acute
obtuse
?
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Complementary and Supplementary
Find the missing angle.
1. Two angles are complementary. One measures
65 degrees. 2. Two angles are supplementary.
One measures 140 degrees.
Answer 25
Answer 40
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Complementary and Supplementary
Find the missing angle. You do not have a
protractor. Use the clues in the pictures.
2.
1.
x
x
55
165
X35
X15
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Vertical Angles
Find the missing angle. You do not have a
protractor. Use the clues in the pictures.
X58
x
58
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More drawings
F
E
20
70
90
D
G
C
70
90
J
20
H
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Final Drawing
B
C
68
60
52
A
G
D
52
60
68
F
E