What is an Acute Angle? - Definition, Description & Examples

What is an Acute Angle? - Definition, Description & Examples
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  • 0:05 What Is an Acute Angle?
  • 0:53 More Acute Angles
  • 1:28 Lesson Summary
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Lesson Transcript
Instructor: Joseph Vigil
In this lesson, you'll learn what makes an angle acute and see a few different examples of them. After the lesson, you can test your new knowledge with a brief quiz.

What is an Acute Angle?

An acute angle is any angle smaller than a right angle. A right angle is an angle that measures 90 degrees. A right angle forms part of a square, which is why it's often depicted by a square at the angle:

a 90 degree angle

So an acute angle is always smaller than the shown angle. Here's an example:

This angle is smaller than 90 degrees.
This angle is smaller than 90 degrees.

The thin blue line indicates where a right angle would be. The angle in black is much smaller than the right angle, so it's clearly acute. It doesn't matter how much smaller an angle is than 90 degrees. Even if an angle measures 89.99999 degrees, it's still acute because it's smaller than 90 degrees.

Consider the following example:

This angle is almost 90 degrees.
a larger acute angle

This angle is much closer to 90 degrees, but it's still smaller, so it's an acute angle.

More Acute Angles

There are several real-world examples of acute angles. A typical pizza slice forms an acute angle:

The angle at the tip is smaller than 90 degrees.
pizza slice

The angle at the slice's tip is smaller than 90 degrees, making it an acute angle. Kitchen tongs also open at an acute angle:

The opening forms an acute angle.
kitchen tongs

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