How is segment notation different from line notation?

Segment notation uses a single overbar above the two endpoint letters, while line notation uses a double-headed arrow above the two point letters. A segment has two endpoints and is finite, whereas a line extends infinitely in both directions.

Conditions

The object is either a segment or a line.
Two points are used for naming.

Reasoning, step by step

For a segment with endpoints X and Y, write $\overline{XY}$ or $\overline{YX}$ using a single bar.
For a line through points X and Y, write $\overleftrightarrow{XY}$ or $\overleftrightarrow{YX}$ using a double-headed arrow.
Recognize that the symbol above the letters distinguishes the finite segment from the infinite line.

Example

The board shows $\overline{XY}$ for a segment and $\overleftrightarrow{XY}$ for a line, with the instructor emphasizing the bar indicates a segment and the arrow indicates a line.

Common misconceptions

Using the same symbol for both segments and lines.
Confusing the single overbar with the double-headed arrow.

Watch the explanation

YouTubeGeometry Lesson 1 - Points, Lines, and Planes

2:58 – 3:26Watch this moment ↗

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