Which is the endpoint of a ray?
The endpoint of a ray is its single starting point — the fixed point where the ray begins before extending infinitely in one direction. In ray AB, the first named point, A, is the endpoint, and the ray passes through B forever.
The answer
A ray has exactly one endpoint: the fixed point where it starts. From that endpoint, the ray extends infinitely in one direction. When a ray is named — for example, ray AB (written with a small arrow over AB) — the first letter is always the endpoint. So in ray AB, point A is the endpoint, and the ray travels out through point B and continues forever past it.
Think of a ray like a beam of light from a flashlight: it has a clear beginning (the bulb) but no end — it just keeps going. That beginning point is the endpoint.
Ray vs. line vs. segment
Geometry defines three related figures, and the number of endpoints is what tells them apart:
- A line extends infinitely in both directions and has zero endpoints. It is named by any two points on it, e.g. line AB, and the order does not matter.
- A line segment is a piece of a line with two endpoints — a definite start and stop. Segment AB has endpoints A and B, and its length can be measured.
- A ray is in between: it has one endpoint and extends infinitely in the other direction. Its length cannot be measured because one end never stops.
So if a question asks how many endpoints a ray has, the answer is one, and the specific endpoint is the point named first in the ray's symbol.
Why naming order matters
Ray AB and ray BA are not the same ray. Ray AB starts at A and goes through B; ray BA starts at B and goes through A — they point in opposite directions. This is different from a line or segment, where AB and BA describe the same figure. Because the endpoint is always written first, the order of the letters carries real meaning for a ray. Whenever you identify "the endpoint," look for the letter that comes first under the ray symbol.
The bigger picture
Rays are the building blocks of angles: an angle is formed by two rays that share the same endpoint, called the vertex. That shared endpoint is why angles have a single corner point. Rays also model many real situations — a sunbeam, the edge of a shadow, or a number line that starts at zero and increases without bound. Recognizing that a ray has one endpoint and one infinite direction helps you correctly name figures, measure what can be measured (segments) versus what cannot (rays and lines), and understand how angles and other shapes are constructed. On a diagram, the endpoint is drawn as a solid dot where the ray begins, while the arrowhead marks the infinite direction — spotting the dot is the quickest way to find the endpoint.
| Line | 0 | Yes — both directions | No |
| Ray | 1 | Yes — one direction | No |
| Line segment | 2 | No | Yes |
Frequently asked
How many endpoints does a ray have?
A ray has exactly one endpoint. That single point is where the ray begins; from there it extends infinitely in one direction, so the other end never stops.
What is the difference between a ray and a line segment?
A line segment has two endpoints and a measurable length. A ray has only one endpoint and extends forever in one direction, so its length cannot be measured.
How do you name a ray correctly?
Name the endpoint first, then any other point the ray passes through, with a small arrow above the letters. In ray AB, A is the endpoint and B shows the direction — so ray AB and ray BA are different rays.
Does a ray have one or two endpoints?
A ray has one endpoint. Two endpoints would make it a line segment, and zero endpoints would make it a line. The single endpoint is the defining feature of a ray.