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Shape, Space and Measure (Intermediate) - Types of Angles and Measurement
 
Types of Angles | Measuring Angles | Written Angle Notation
Types of Angles

Acute angles are angles less than ninety degrees.

For Example:
The angles below are acute angles.
angles and measurement1
Obtuse Angles are angles greater than 90o and less than 180o
 
For Example:
The angles below are obtuse angles.
angles and measurement2
Right Angle is an angle of 90o
 
For Example:
The angles below are right angles.
angles and measurement3
The Straight Line. This is an angle of 180o, as shown below.
angles and measurement4
Reflex Angles These are angles greater than 180o and less than 360o
 
For Example:
The angle below is a reflex angle.
angles and measurement5

Measuring Angles

We use a Protractor for measuring angles in degrees. Below is a picture of a protractor and how we use it. Place the centre of the zero line above the angle at A, the zero line should be covering one side of the angle. Starting at zero follow the scale around to the other side of the angle and read off the number of degrees. 41o in the angle below.

Note: we are using the inside scale because it is the one which starts at zero. (The outside scale starts at 180o).

If we were measuring the angle on the other side, starting from the left, then we would use the outside scale and the result would be 139o.

ang_meas1

 
Note: Place the centre of the zero line here and start at zero on the scale. To measure the angle of 41o.
Circular protractors, where the scale goes up to 360o
 

Written Angle Notation
 

Angles are written in the following ways:

1) Using three capital letters, with the angle sign over the middle letter.
angles and measurement7
2) Using a small letter inside the angle.
angles and measurement8
Either of these methods can be used in problems on angles.