# Ray

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

, contains all of the points on line 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

is not the same as ray .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.

### 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.