Objective
To understand basic terms and postulates of geometry
In this lesson, you will learn basic geometric facts to help you justify your answer to the Solve It.
Essential Understanding Geometry is a mathematical system built on accepted facts, basic terms, and definitions.
In geometry, some words such as point, line, and plane are undefined. Undefined terms are the basic ideas that you can use to build the definitions of all other figures in geometry. Although you cannot define undefined terms, it is important to have a general description of their meanings.
Term Description | How to Name It | Diagram |
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A point indicates a location and has no size. | You can represent a point by a dot and name it by a capital letter, such as A. | |
A line is represented by a straight path that extends in two opposite directions without end and has no thickness. A line contains infinitely many points. | You can name a line by any two points on the line, such as
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A plane is represented by a flat surface that extends without end and has no thickness. A plane contains infinitely many lines. | You can name a plane by a capital letter, such as plane P, or by at least three points in the plane that do not all lie on the same line, such as plane ABC. |