Mathematics
Grade 9
15 min
Lines, line segments, and rays
Lines, line segments, and rays
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1
Introduction & Learning Objectives
Learning Objectives
Define and visually differentiate between a line, a line segment, and a ray.
Correctly name lines, line segments, and rays using proper geometric notation.
Identify and model these geometric figures in diagrams and real-world contexts.
Understand and apply the concept of collinear points and the Segment Addition Postulate.
Calculate the midpoint of a line segment on a coordinate plane using the Midpoint Formula.
Calculate the length of a line segment on a coordinate plane using the Distance Formula.
How does your phone's GPS calculate the straight-line distance between two locations? 🗺️ It all begins with the fundamental geometric concepts of points and the paths that connect them!
This tutorial will explore the essential building blocks of all geom...
2
Key Concepts & Vocabulary
TermDefinitionExample
LineA one-dimensional figure made up of a straight path of points that extends infinitely in opposite directions. It has no thickness and no endpoints.A line passing through points A and B is denoted as ↔AB. The arrows indicate it continues forever in both directions.
Line SegmentA part of a line that is bounded by two distinct endpoints. It contains these endpoints and all the points on the line between them. A line segment has a specific, measurable length.A line segment with endpoints A and B is denoted as AB (with a bar over it). Its length is denoted as AB.
RayA part of a line that has one endpoint and extends infinitely in one direction. The endpoint is always named first.A ray starting at point A and passing through point B is denoted as →AB. It starts at A a...
3
Core Formulas
Segment Addition Postulate
If three points A, B, and C are collinear and B is between A and C, then AB + BC = AC.
Use this postulate to find the length of a part of a segment or the whole segment when you know the lengths of the other parts. It essentially states that the two smaller pieces add up to the whole.
Midpoint Formula
For a line segment with endpoints (x₁, y₁) and (x₂, y₂), the midpoint M is given by the formula: M = ( (x₁ + x₂)/2 , (y₁ + y₂)/2 ).
Use this formula in coordinate geometry to find the exact center point of a line segment. It works by averaging the x-coordinates and averaging the y-coordinates.
Distance Formula
The distance, d, (or length) of a line segment with endpoints (x₁, y₁) and (x₂, y₂) is given by the formula: d = \sqrt{(x₂ - x₁)² + (y₂ -...
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Sign Up Free to ContinueSample Practice Questions
Easy
Which of the following best describes a line in Euclidean geometry?
A.part of a line that is bounded by two distinct endpoints.
B.figure that has one endpoint and extends infinitely in one direction.
C.straight path of points that extends infinitely in two opposite directions and has no thickness.
D.set of points that all lie on the same plane.
Easy
Which is the correct geometric notation for a line segment with endpoints X and Y?
A.↔XY
B.XY
C.→XY
D.XY
Easy
A ray is best defined as...
A.part of a line with one endpoint that extends infinitely in one direction.
B.part of a line with two distinct endpoints.
C.collection of collinear points with a measurable length.
D.one-dimensional figure that extends infinitely in two directions.
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