Points, Lines, and Planes
LESSON 1-3
Undefined Terms
In math we have three undefined terms that are
so basic we use those to define all the other
shapes.
What are those terms?
GEOMETRY
Vocabulary
Point: It has location and nothing else. No size. No
height. No depth. No friends.
A
Line: A straight, unbroken set of points that goes
on forever. It has infinite length but no
thickness.
m
B
AB
BA
Line m
A
Plane: A surface with length and width but no
thickness.
GEOMETRY
Points, Lines, and Planes
LESSON 1-3
Notation
Planes are usually drawn as a parallelogram.
Planes are denoted in one of two ways.
plane ABC or plane BCA
Note with four or more points you still choose any three or
more in any order.
A
C
B
M
plane M. So uppercase cursive M. Notice M
does not refer to a point on the plane.
GEOMETRY
Example: Point, line, plane.
Talk to a neighbor, a friend, a loved one, or yourself. Give us
two examples of points, lines, and planes.
GEOMETRY
Vocabulary
Line Segment: A line that has two endpoints.
A
Ray:
B
AB
BA
A line with ONE endpoint.
A
Y
B
AB
Collinear: Points in the same line
AY
F
Z
P
Coplanar: Points on the same plane
GEOMETRY
Example:
Which tennis balls are collinear? Which sets of three
are coplanar?
GEOMETRY
Example:
Which points are collinear? Which sets of three are
coplanar?
.. .
..
.
D
A
C
E
B
F
GEOMETRY
Points, Lines, and Planes
LESSON 1-3
You Try #1
Since F, P, and C do not lie on the same line, they are not collinear.
GEOMETRY
Points, Lines, and Planes
LESSON 1-3
You Try #2
Since F, C, and E are points on line m, any combination of two in any order
would be a correct way to name the line. So D is the correct answer.
GEOMETRY
Points, Lines, and Planes
LESSON 1-3
You Try #3
Since E, F, G and H are all points on the top of the plane any three or more
of these points in any order would be correct. So C, FGH is the correct answer.
GEOMETRY
Points, Lines, and Planes
LESSON 1-3
Vocabulary
Postulate
(or axiom)
An accepted statement
of fact. A statement
accepted without proof.
GEOMETRY
Points, Lines, and Planes
LESSON 1-3
Postulates
How many different lines can you draw
A
between these two points?
B
GEOMETRY
Points, Lines, and Planes
LESSON 1-3
Postulates
Any time you have three noncollinear points
there is only one plane that you can
draw around the points.
A
B
C
GEOMETRY
Points, Lines, and Planes
LESSON 1-3
Example:
Use the diagram below. What is the intersection of plane HGC and
plane AED?
The back and left faces of the cube intersect at HD.
Planes HGC and AED intersect vertically at HD.
GEOMETRY