Identify lines and rays

A line is a straight path with no endpoints, extending indefinitely in both directions, while a ray has one endpoint and extends indefinitely in one direction; a line segment has two endpoints and finite length. These objects are identified in diagrams by their endpoint markers and arrowheads, regardless of orientation, while recognizing that a drawing represents an ideal object rather than a physically finite path; coordinate equations, angle measurement, and formal geometric proofs are beyond this scope.

Detailed Explanation: Identify lines and rays

Look at the ends of the path. The marks at the ends tell you what kind of geometric object it is.

Line: has arrowheads at both ends. It continues forever in both directions.
Ray: has one endpoint, shown by a dot, and one arrowhead. It continues forever in one direction.
Line segment: has two endpoints, usually shown by dots. It has a definite length.

Worked example

Suppose a diagram shows these three paths:

1.  <------ P ---------------- Q ------>

2.  R •------------------------ S ------>

3.  T •------------------------ U •

Identify each one by checking its end marks.

The first path has two arrowheads. It is a line.
The second path has one dot and one arrowhead. It is a ray.
The third path has two dots and no arrowheads. It is a line segment.

Remember: The picture may look short because it is drawn on paper, but an arrow means the path keeps going forever. The direction of the picture does not matter. What matters is the number of endpoints and arrowheads.

Learn by doing: Identify lines and rays

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Identify Lines, Segments, and Rays

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