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

2. Undefined Terms Definition of words Philosophy Class?
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 Y Use the diagram to answer each question.Z Y V
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.

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

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