Detailed definition
Understanding Line Segment
Line Segment is the portion of a line that begins at one endpoint and ends at another. A line segment has two endpoints and a finite length. Unlike a full line, a segment has a definite length and can be measured.
The endpoints are not decoration. They are what make the figure finite. If the straight path continues past either endpoint, the diagram has changed into something else.
Segment language appears everywhere in school geometry: side lengths of triangles are segments, diagonals of polygons are segments, and many early theorems compare or add segment lengths.
Key facts
Important ideas to remember
- A line segment has two endpoints and a finite length.
- A segment has exactly two endpoints.
- A segment is straight and finite, so its length can be measured.
- Segment notation names the whole bounded part from one endpoint to the other.
Where it is used
Where line segment shows up
- Use line segment when measuring distance between two points in a diagram.
- Use it when naming triangle sides, polygon sides, diagonals, and chords.
- Use it in midpoint, bisector, and segment-addition problems where finite length matters.
Common mistakes
What to watch out for
- Do not let the line continue past the endpoints if the figure is meant to be a segment.
- Do not forget that the endpoints belong to the segment itself.
- Do not confuse the visual length of the drawing with a labeled measurement unless the scale is known.