# What is a Straight Angle? - Definition & Example

Coming up next: What is an Obtuse Angle? - Definition & Examples

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• 0:00 What Is A Straight Angle?
• 0:44 Line Of Sight
• 1:05 How Does A Straight…
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Lesson Transcript
Instructor: Flint Johnson

Flint has tutored mathematics through precalculus, science, and English and has taught college history. He has a Ph.D. from the University of Glasgow

This lesson will be an explanation of what a straight angle is. It will include several examples that fully demonstrate the straight angle in contrast with other angles.

## What Is a Straight Angle?

A straight angle is just a mathematical way of saying a straight line. Basically, it's a perfectly straight line with no bending or even the slightest change in angle. In mathematical terms, it is a line with no changes in angle. Any line will do: the sides of a bookshelf, the surface of a floor or ceiling. Even an imaginary line along your own line of sight would be considered a straight angle. A straight angle doesn't need to have endpoints to be a straight line. It can, such as the sides of a bookshelf. However, a straight line can also be a ray extending to one or both sides.

## Line of Sight

Your line of sight is basically the imaginary line between your eye and whatever you are looking at. It might seem strange, but your line of sight is probably the best example of a straight angle because it cannot be deviated by gravity, the influence of a tool, or anything else. It must be exactly straight because that is how we see things.

## How Does a Straight Angle Fit In?

In mathematics, there are several kinds of angles. Acute angles are smaller than 90 degrees, whereas those greater than 90 degrees but less than 180 are considered obtuse. Those greater than 180 degrees are called reflex angles. There are also more important, specific angles that have special names. For example, the right angle is exactly 90 degrees. It's important because it makes much of trigonometry possible such as sine, cosine, and tangent that comes with it. The Pythagorean Theorem comes into play with a right triangle as well.

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