What if you wanted to group different angles into different categories? After completing this Concept, you'll be able to classify angles geometrically.
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CK12 Foundation: Chapter1AngleClassificationA
James Sousa: Animation of Types of Angles
Guidance
By looking at the protractor we measure angles from
Straight Angle: When an angle measures
Right Angle: When an angle measures
Notice the halfsquare, marking the angle. This marking is always used to mark right, or
Acute Angles: Angles that measure between
Obtuse Angles: Angles that measure between
It is important to note that
Any two lines or line segments can intersect to form four angles. If the two lines intersect to form right angles, we say the lines are perpendicular.
The symbol for perpendicular is
There are several other ways to label these two intersecting lines. This picture shows two perpendicular lines, four right angles, four
Example A
Name the angle and determine what type of angle it is.
Example B
What type of angle is
Example C
What type of angle is
Watch this video for help with the Examples above.
CK12 Foundation: Chapter1AngleClassificationB
Vocabulary
A straight angle is when an angle measures
Interactive Practice
Practice
For exercises 15, determine if the statement is true or false.
 Two angles always add up to be greater than
90∘ . 
180∘ is an obtuse angle. 
180∘ is a straight angle.  Two perpendicular lines intersect to form four right angles.
 A right angle and an acute angle make an obtuse angle.
For exercises 611, state what type of angle it is.

55∘ 
92∘ 
178∘ 
5∘ 
120∘ 
73∘  Interpret the picture to the right. Write down all equal angles, segments and if any lines are perpendicular.
 Draw a picture with the following requirements.
In 14 and 15, plot and sketch

A(5,−3),B(−3,−1),C(2,2) 
A(−3,0),B(1,3),C(5,0)