The Lesson
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.
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:
Interactive Game on the Types of Angles
Here is an interactive game to help you learn about the types of angles.
- Click on an angle so it drops into the correct "bucket."
- In total, there are 10 angle to clear.
- If an angle drops into the wrong "bucket," you will lose one of your three lives.
- Good luck!
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.
Drag and Drop Game
Here is a
drag-and-drop game to help you learn about the types of angles.