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Types of Angles (Mathematics Lesson)

Types of Angles

Angles can be classified as acute, right, obtuse, straight, reflex or full.

Acute Angles

An acute angle is an angle of less than 90°.



Read more about acute angles

Right Angles

A right angle is an angle of 90°.



(Note: Right angles are often denoted by adding a small right angle that forms a square with the angle.)

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Obtuse Angles

An obtuse angle is an angle greater than 90° and less than 180°.



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Straight Angles

A straight angle is an angle of 180°.



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Reflex Angles

A reflex angle is an angle greater then 180° and less than 360°.



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Full Angles

A full angle is an angle of 360°.



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Note
WHAT IS AN ANGLE?

An angle is created by two rays that have a common end point, called the vertex.



WHO CLASSIFIED ANGLES?

Euclid classified angles in his book, Elements.



Definition 10: "When a straight line standing on a straight line makes the adjacent angles equal to one another, each of the equal angles is right".

Definition 11: "An obtuse angle is an angle greater than a right angle".

Definition 12: "An acute angle is an angle less than a right angle".

OBLIQUE ANGLES

Acute and obtuse angles are also oblique angles. Oblique angles are neither right angles nor multiples of right angles.