Detailed definition
Understanding Ray
Ray starts at one endpoint and extends forever in one direction. A ray has one endpoint and extends infinitely in one direction. That makes it different from both a line, which extends in two directions, and a segment, which stops in two places.
The naming order matters with rays. In ray AB, point A is the endpoint and point B shows the direction. Reversing the letters names a different ray if the figure is not symmetrical.
Rays are the sides of angles, they appear in constructions, and they help describe direction in a way a finite segment cannot. Reading them correctly early saves many later angle mistakes.
Key facts
Important ideas to remember
- A ray has one endpoint and extends infinitely in one direction.
- A ray has one endpoint and no second endpoint.
- The arrow belongs at the extending end, not at the endpoint.
- Ray notation depends on order: the first named point is the endpoint.
Where it is used
Where ray shows up
- Use ray when describing the sides of an angle.
- Use it in constructions where one point is fixed and the direction continues beyond the board.
- Use it when direction matters but a finite stopping point does not.
Common mistakes
What to watch out for
- Do not draw closed dots at both ends and still call the figure a ray.
- Do not place the arrowhead behind the endpoint instead of on the extending side.
- Do not reverse the ray name without checking which point is supposed to be the endpoint.