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FF.1 Identify lines, line segments, and rays

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What is a line?

Line: A line is a straight path of points that goes on forever in both directions. It has no endpoints.

How to identify:
  • Look for a straight path with arrows on both ends.
  • It has no beginning and no end.
Examples:
  • A straight road that continues without stopping.
  • In math diagrams, lines are usually drawn with arrows at both ends (↔).
Note

A line is endless—you can always imagine it going farther in both directions.

What is a line segment?

Line Segment: A line segment is a part of a line that has two endpoints. It does not go on forever.

How to identify:
  • Look for a straight path with dots or points marking both ends.
  • It starts and stops at those two endpoints.
Examples:
  • The edge of a desk.
  • In math diagrams, segments are shown with two endpoints (──).
Note

A line segment is the shortest distance between two points.

What is a ray?

Ray: A ray is a part of a line that starts at one endpoint and goes on forever in one direction.

How to identify:
  • Look for a straight path with one endpoint and an arrow on the other end.
  • It begins but does not end.
Examples:
  • Sunlight shining from the sun.
  • In math diagrams, a ray is drawn with one endpoint and one arrow (•→).
Note

A ray always has a starting point but never an ending point.

Comparing lines, line segments, and rays

Although they all look like straight paths, lines, line segments, and rays are different because of their endpoints.

Quick guide:
  • Line: goes on forever in both directions (↔).
  • Line Segment: has two endpoints (──).
  • Ray: starts at one endpoint and goes on forever in one direction (•→).
Note

Always look at the endpoints (or arrows) to decide whether it is a line, segment, or ray.

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