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1.2 Points, Lines and
Planes
Geometry
Mrs. Lutz
Mrs. Sant
Mrs. Berrett
Objective

Understand and use geometry terminology
such as
– Point
– Line
– Plane
– Collinear points
– Midpoint
– Line Segment
-
Ray
Opposite rays
Infinite
Parallel
Perpendicular
Example what your note page
should look like now
1.2 Points,
Lines, &
Planes
Objectives:
Name____________________________
Date___________________Period_____
Class_____________________________
Points
Point A
• A point has no dimension.
It is usually represented by a small dot.
• You can think of a point as a location.
• Points are named by a capital letter.
A
Lines
• A line extends in two opposite directions.
l
• Name a line with two points or
A
a single lowercase letter.
• A line has one-dimension.
B
Line
l
or AB
Collinear Points

Collinear points are points that lie
on the same line.

Points A, C, and B are collinear points.
A
C
B
Ex. 1: Naming Collinear Points
Name three points that are collinear
H
G
D
Solution:
D, E and F lie on the same line, so they are collinear.
E
Ex. 2: Naming Collinear Points
Name three points that are not collinear.
H
G
D
E
Solution:
There are many correct answers.
For instance, points H, E, and G do not lie on the same line.
Planes
• A plane extends in two dimensions.
A
• A plane is usually represented by a shape
that looks like a tabletop or wall.
M
C
B
Plane M or plane ABC
• Imagine that the plane extends without
end, even though the drawing of a plane
appears to have edges.
Coplanar

Coplanar means together on
the same plane.
A
Points A, B and C are coplanar.
M
C
B
Skewed Lines

Skewed lines are not in the same plane
and do not intersect.
Inifinite
l.

Consider the line

How many points are there
between A and B?
l
B
There are an infinite number of points
between two points.
Line
A
l
Line Segments A
B
Segment AB

The line segment or segment AB (symbolized by AB)
is named by its endpoints.
The line segment includes points A and B and
all points in between.
Rays
A
B
Ray AB

The ray AB (symbolized by AB) is named by its
endpoint and a second point B.

The ray contains point A and all points to the
right on AB.
l
More . . .

B
Note that AB is the same as BA
and AB is the same as BA.
A
Line

l or AB
AB and BA are not the same.
They have different starting points
and extend in different directions.
A
B
Ray AB
A
B
Ray BA
Opposite Rays

l
Opposite rays are two collinear rays
that share an endpoint.
B
C
A
Line

If C is between A and B,
then CA and CB are opposite rays.
l or AB
Parallel Lines

Lines that do not intersect.
Line
l
ll
Line
m
Line
l
Line
m
Perpendicular Lines
Lines that intersect
at a 90o angle.
Line
l
т

Line
Line
m
m
Line
l
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