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Acute Angles (Mathematics Glossary)

What Is an Acute Angle?

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

acute angle

An angle less than a right angle is an acute angle.

Dictionary Definition

The Oxford English Dictionary defines an acute angle as "a plane angle: less than 90 degrees."

Real Examples of Acute Angles

The angles below are all acute angles:

examples of acute angles. 75 degrees, 30 degrees and 89 degrees
Geometry Lessons
Interactive Test

Here's a second test on acute angles.
Here's a third test on acute angles.


What's in a Name?

Acute comes from the Latin word 'acutus' meaning "sharp".

An acute angle makes a sharp point.

Euclid and Acute Angles

Euclid defines angles in his book, Elements.

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

Acute Triangles

Acute triangles are triangles that have all acute angles.

acute triangle

Other Types of Angles

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