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".
Acute and obtuse angles are also oblique angles. Oblique angles are neither right angles nor multiples of right angles.
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Use this interactive widget to learn about the types of angles. Start by clicking in the shaded area.