The way you look at this computer screen is not the only angle in your life. Like everyone else, you are surrounded by angles. Even the rays of the sun reach you, and every other object on Earth, at an angle that determines important aspects of your life, such as the amount of light and heat you experience at any given moment.

Angles are the basic components of many geometric shapes as well. By definition, an angle is a shape formed by two rays diverging from a common point known as the vertex.

These rays are the "sides" of an angle, known as the initial side—also called the base of an angle—and the terminal side. The angle is formed at the point where the two sides meet, the vertex. The curve around the vertex point in the diagram below is used to show how wide the angle is or how much "incline" the angle has.

In geometry and other math subjects, you can describe an angle by writing or saying its vertex point with an angle symbol in front of it, like \(\mathsf{ \angle }\)A. Another way to refer to a specific angle is to write all three capital letters representing the rays and vertex that form the angle. For example, \(\mathsf{ \angle }\)CAB or \(\mathsf{ \angle }\)BAC indicate the same angle as \(\mathsf{ \angle }\)A. Notice that you can use any arrangement of letters as long as the letter of the angle's vertex is in the middle.

Angles can be positive or negative. In a positive angle, the terminal side inclines counterclockwise from the initial side. In a negative angle, the terminal side inclines clockwise from the initial side.

Positive Angle

Negative Angle

In this lesson, you will learn how to identify and measure different types of angles. You will also learn how to draw an angle based on a measurement.