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What is an Obtuse Angle? - Definition & Examples

What is an Obtuse Angle? - Definition & Examples
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  • 0:05 Definition
  • 0:26 Right Angles
  • 0:52 Obtuse Angles
  • 1:42 A Special Obtuse Angle
  • 2:13 Lesson Summary
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Lesson Transcript
Instructor: Joseph Vigil
In this lesson, you'll learn what angles, right angles, and obtuse angles are; you'll see a few examples of different obtuse angles. Test your knowledge with a brief quiz once you've completed the lesson.

Definition

An angle is the space that forms in the corner whenever two line segments meet.

Example of an Angle

The small curved line in the corner is a standard notation that represents an angle. Here is another angle:

Another Angle

Although the two examples are clearly quite different, they're both still angles by definition because they show the space that forms when two line segments meet.

Right Angles

To talk about obtuse angles, it'll help us to define right angles. A right angle is one that measures exactly 90 degrees. A right angle is easy to spot because it forms a perfect square.

Example of a Right Angle

These are common angles because there are many times when people are building something and want a square corner. Imagine the rooms of your home, your doors or table corners without right angles!

Obtuse Angles

Obtuse angles are simply angles larger than 90 degrees. We can spot them because they extend past what would be a right angle.

Imagine tilting a car seat back so that you can lie down comfortably. You'd push it past the upright position, closer to lying flat. Where the seat's bottom and back meet would be an obtuse angle because you've pushed the back beyond a 90 degree angle. It might look something like this:

An Obtuse Angle Goes Beyond 90 Degrees

The dashed line indicates a right angle. The seat's back is clearly pushed beyond that point, forming an obtuse angle.

Obtuse angles don't have to be that dramatic, however. As long as the angle measures over 90 degrees, it's obtuse, including this more subtle one:

As long as the angle is larger than 90 degrees, it

Although this angle barely goes beyond 90 degrees, it's still obtuse by definition.

A Special Obtuse Angle

How about this one?

A Straight Line

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