Theory:

When two rays diverge from a common point, they are called angles.
The rays which form an angle are called the angle arms, and the common point is called the angle vertex.

There are various types of angle, such as acute angle, right angle, obtuse angle, straight angle and reflex angle. We may summarize them up as follows:

Acute angle: An angle is called an acute angle whose measure is less than \(90°\).
 
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Right angle: An angle is called a right angle whose measure is exactly \(90°\). It looks like the corner of a square.
 
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Obtuse angle: An angle is an obtuse angle whose measure is greater than \(90°\).
 
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Straight angle: An angle is called a straight angle whose measure is exactly \(180°\).
 
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Reflex angle: An angle is called a reflex angle whose measure is greater than \(180°\) and less than \(360°\).
 
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