A ray is a part of a line that has one endpoint and extends infinitely in one direction from the endpoint.

In the figure above, ray AB, written symbolically as AB, contains all of the points on line AB from A in the directions of B.

The following are some examples of rays:

1. A laser pointer creates a ray of light.

2. The number line showing whole numbers is really not a line, but a ray. It begins at the endpoint, 0, and extends infinitely through 1 because there is no greatest whole number.

3. In coordinate geometry, an inequality can be represented as a ray on a number line.

The inequality x≥-1 can be represented by the ray above, whose endpoint is at -1 on the real number line.

Naming rays

A ray has a directional component so be careful how you name it. Ray AB is not the same as ray BA.

A ray with 3 labeled points can be named in different ways, as shown below. Just make sure to include the endpoint.

Angles and rays

An angle is formed when two rays share a common endpoint.

Rays AB and BC share endpoint B and form the sides of ∠ABC.

Did you know?

A ray of sunshine begins at the sun (the endpoint) and travels through space in one direction. A ray from the sun can be used as a model for thinking about a ray in geometry.

See also line, line segment.