This document defines basic geometry terms like point, line, and plane which are undefined terms that serve as building blocks. It also introduces defined terms like segment and ray. Postulates are accepted statements of fact in geometry, such as through any two points there is exactly one line. The document provides examples applying these terms and postulates to identify collinear points, coplanar lines, and intersecting planes.

1. 1-2: Points, Lines, and
Planes
Basic Geometry Terms

2. Undefined Terms
 Definition of words
 Consist of other words
 How do you define the first word?
 Philosophy Class?
 Every end has a start
 Every effect has a cause
 Geometry undefined terms
 Point, line, and plane
 Used to build the definitions of other figures

3. Undefined Terms
 Point – indicates a location and has no size
 Line – represented by a straight path that
extends in two opposite directions without end
and has no thickness. A line contains infinitely
many points.
 Plane – represented by a flat surface that
extends without end and has no thickness. A
plane contains infinitely many lines.

4. Undefined Terms
 Collinear Points – points that lie on the same line
 Coplanar – when points and/or lines lie on the same plane

5. Defined Terms
 Segment – part of a line that consists of two endpoints and all points between
them.
 Ray – part of a line that consists of one endpoint and all the points of the line
on one side of the endpoint
 Opposite rays – two rays that share the same endpoint and form a line

6. Example
 Use the diagram to answer each question.
- Name two coplanar lines.
- Name three non-collinear points.
- Name the plane two different ways.
- Name a pair of opposite rays.
W
X
Z
Y
V

7. Take Home Message
 Undefined terms are used as building blocks of Geometry (and Math)
 Geometry will have a lot of vocabulary words
 The concepts will give us algebraic equations
 Geometry will enhance our artistic abilities

8. 1.2 Continued
 Postulate – accepted statement of fact
 Like undefined terms, used as building blocks of the logical system in geometry
 Also known as axioms
 Postulate 1.1- through any two points, there is exactly one line
 Postulate 1.2- if two distinct lines intersect, then they intersect in exactly
one point.

9. 1.2 Continued
 Postulate 1.3- if two distinct planes intersect, then they intersect in exactly
one line

10. 1.2 Continued
 Postulate 1.4 – through any three noncollinear points, there is exactly one
plane

11.  Where does Plane ABCD intersect
Plane ACEG?
 What plane contains the points
C, D, and B?
 What plane contains the points
E, F, and C?
Example
A
C
B
E
G
F
H
D

12. Take Home Message
 Postulates are assumed to be true
 No formal proof
 Relationship between dimensions
 A point is the intersection of two lines
 A line is the intersection of two planes
 A plane is the intersection of 3D figures