Lines, Segments, and Rays
Lines, segments, and rays are the three fundamental one-dimensional objects in geometry studied in Grade 6 math (Saxon Math, Course 1). A line extends infinitely in both directions and is named by two points or a lowercase letter (line AB or line l). A line segment has two endpoints and a definite length; named by its endpoints (segment AB or AB̄). A ray has one endpoint and extends infinitely in one direction; named by its endpoint first (ray AB or AB→). Two rays sharing an endpoint form an angle. These three objects are the building blocks for all geometric figures and are used to define angles, polygons, and other shapes.
Key Concepts
New Concept A segment is part of a line and has two endpoints. A mathematical line has no endpoints. A ray has one endpoint. What’s next Now that you know the definitions, you'll get hands on practice. Next, you'll use rulers to measure the length of line segments in both inches and centimeters.
Common Questions
What is the difference between a line, a line segment, and a ray?
A line extends infinitely both ways (no endpoints). A segment has two endpoints (finite length). A ray has one endpoint and extends infinitely in one direction.
How do you name a line segment?
By its two endpoints with a bar over them: AB̄. Order doesn't matter: AB̄ = BĀ.
How do you name a ray?
By its endpoint first, then another point on the ray: ray AB means start at A, go through B and beyond. Order matters — ray BA starts at B.
How many endpoints does each geometric object have?
A line: 0 endpoints. A segment: 2 endpoints. A ray: 1 endpoint.
How do two rays form an angle?
When two rays share a common endpoint (vertex), the space between them is an angle. The size of the opening determines the angle measure.