Angle: An Illustrated Classification

The applet below illustrates the common classification of angles. It works with regular and signed angles.

For unsigned angles,

• An angle is zero if its two sides coincide and its interior is empty.
• An angle is full if its two sides coincide and its interior is the whole plane with a ray removed.
• An angle is straight if its two sides form a straight line. Either of the so formed half-planes may be the interior of the angle.
• An angle is right if when doubled it makes one straight angle.
• An angle less than right is acute.
• An angle less than straight but greater than right is obtuse.
• An angle between straight and full is reflex.

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Copyright © 1996-2008 Alexander Bogomolny