Lesson 1-2
Points, Lines,
Planes
Lesson 1-1 Point, Line, Plane
1
Points

Definition: Points do not have actual size. It can be
thought of as a location
A

Naming/Notation:
B
C
A
Use capital letters

Picture/Notes:
Using dots
Note: Never name two points with the same letter
(in the same sketch).
2
Lines


Definition: A series of points that extends in two opposite
directions, without end.
Picture/Notes: using arrows at both ends.
n
A
B


C
Naming/Notation: 2 ways
(1) small script letter – line n
AB , BC, AC , BA, CA, CB
(2) any two points on the line ABC
Never name a line using three points 3
Planes
Definition: A plane is a flat surface that has no thickness and
extends indefinitely in all directions.
 Picture/Notes: Use a quadrilateral (four sided figure)
 Naming/Notation: 2 ways
(1) Capital script letter – Plane M

(2) Any 3 non collinear points in the plane - Plane: ABC/ ACB /
BAC / BCA / CAB / CBA
A
B
M
C
Horizontal Plane
Vertical Plane
Other
4
Space

Definition: The set of all points.
5
Collinear Points

Definition: Collinear points are points that lie on the same line.
(The line does not have to be visible.)
Naming/Notation:
 Points A, B and C are collinear.
A
B
C
Collinear
C
Picture/Notes:
*Points that do not lie on the same
are noncollinear. Lesson 1-1 Point, Line, Plane
A
B
line Non collinear
6
Coplanar
Definition: Coplanar objects (points, lines, etc.) are
objects that lie on the same plane. The plane does not
have to be visible.
Picture/Notes: Are the following
A
D
B
C
E
H
F
G
points coplanar?
A, B, C ?
A, B, C, F ?
H, G, F, E ?
E, H, C, B ?
A, G, F ?
C, B, F, H ?
Yes
No
Yes
Yes
Yes
No
7
Postulate (axiom)

Definition: An accepted statement of
fact.

Used to identify geometric properties
using the undefined and defined terms.
Lesson 1-1 Point, Line, Plane
8
Postulate 1-1

Through any two points there is exactly
one line.
• Naming/Notation: Line t is the only line that
passes through points A and B.
• Picture:
B
t
A
Lesson 1-1 Point, Line, Plane
9
Postulate 1-2


If two lines intersect, then they intersect
in exactly one point.
Naming/Notation:
• AE and BD intersect at C.
B
A
Picture:
C
E
D
Lesson 1-1 Point, Line, Plane
10
Postulate 1-3

If two planes intersect then they
intersect in exactly one line.
• Naming/Notation: Plane RST and plane STW
intersect in ST
Picture:
R
W
S
T
11
Postulate 1-4

Through any three noncollinear points
there is exactly one plane.
Lesson 1-1 Point, Line, Plane
12
Practice Problems
 After
copying the definitions
down..
 Complete page 3 in your
packet EVENS ONLY!!!
Lesson 1-1 Point, Line, Plane
13