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What Is an Obtuse Angle? (Mathematics Lesson)

What Is an Obtuse Angle?

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



An obtuse angle is greater than a right angle and less than a straight line.

Real Examples of Obtuse Angles

The angles below are all obtuse angles:



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Note
WHAT'S IN A NAME?

Obtuse comes from the Latin word 'obtusus' meaning "blunt".

An obtuse angle makes a blunt point.

EUCLID AND OBTUSE ANGLES

Euclid defines angles in his book, Elements.

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

OBTUSE TRIANGLES

Obtuse triangles are triangles that have an obtuse angle.



OTHER TYPES OF ANGLES

Obtuse angles are one type of angle, the other types are acute, right, straight, reflex and full.