The Lesson

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

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

Dictionary Definition

The Oxford English Dictionary defines an obtuse angle as "a plane angle: greater than 90 degrees and less than 180 degrees."

Real Examples of Obtuse Angles

The angles below are all obtuse angles:

example of obtuse angles. 135, 160 and 91 degrees.

Interactive Game on the Types of Angles

Here is an interactive game to help you learn about the types of angles.

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.

an obtuse triangle

Drag and Drop Game

Here is a drag-and-drop game to help you learn about the types of angles.