1.2 Points, Lines, and Planes
What is a definition?

Known words used to describe a new word
Undefined terms – are terms not formally
defined.
There are three undefined terms in geometry:
1. Point
2. Line
3. Plane
Point
1. A location in space.
2. Has no dimension (no length, no width,
no depth).
3. Usually represented by a dot.
4. Named using one capital letter.
5. All geometric figures consist of points
 POINTS ARE TO GEOMETRIC FIGURES AS
___________ IS TO HUMANS?
Point
For example:
●B
What would be a real world example of a point?
Line
1.
2.
3.
4.
5.
A series of points that extends in opposite
directions without end.
One-dimensional (length).
Has an arrowhead on each end
representing the fact that it goes on
forever.
Always straight.
Named with a lowercase script letter or by
2 points on the line
Line
For example:
Can be called:
l
A
B
Line l
Line AB or AB
Line BA or BA
Real World example?
Plane
1.
2.
3.
4.
A flat surface that extends forever in two
dimensions (length & width).
Contains infinitely many points and lines.
Usually represented by a four-sided
figure.
Named with a capital script letter or 3
points on the surface of the plane
Plane
For example:
W
A
B
C
Can be named:
Plane W
Plane ABC, plane BCA, plane
CBA, etc.
**Planes can be named by more
than 3 points, but they must be
Real World example?named in either a clockwise or
counter-clockwise manner

Horizontal Planes – Ceiling and Floor

Horizontal Planes – Two sides horizontal and
no sides vertical


Vertical Planes – Walls
Vertical Planes – two sides are vertical
More Definitions

Collinear points –
points that can lie on the same
line.
**Think of the suffix “CO” as sharing.**
More Definitions

Noncollinear points –
D
More Definitions

Coplanar points – What does it mean?
points that can lie on the same plane.
More Definitions


If the points do not lie in the same plane they
are?
Noncoplanar points –
A
D
More Definitions

Equidistant – equally distant
REMOTE TIME !
Classify each statements as true or
false
Question 1

PF ends at P
Question 2

Point S is on an infinite number of lines
Question 3

A plane has no thickness
More Definitions

Intersect –
–
–

Two or more figures intersect if they have one or
more points in common.
Think “meet” or “Cut”
Intersection –
–
–
All points or sets of points the figures have in
common.
Depending on what is intersecting, the
intersection will be different
When a line and a point intersect,
their intersection is a point.
l
B
Like taking a road trip and
driving through a certain town
or city on the map.
When 2 lines intersect, their
intersection is a point.
Like the intersection of
Foothill and Ramsdale
When 2 planes intersect, their
intersection is a line.
The planes
are cutting
through one
another
When a line and plane intersect, their
intersection is a point.
Like sticking a pencil
through a piece of paper
Questions???
Question 4

Collinear points are coplanar
Question 5

Planes have edges
Question 6

Two planes intersect in a line segment
Question 7

Two intersecting lines meet in exactly one point
Question 8

Points have no size
Question 9

Line XY can be denoted as XY or YX.
Partner Share: True or False

All points on a line are coplanar
True or False

A line has one endpoint
True or False

A point is named by a capital letter.
True or False

Two lines intersect in two points.