Section 1-3: Segments, Rays, Parallel Lines, Planes
SPI 32A: Identify properties of plane figures
Objectives:
• Identify segments and rays
• Recognize parallel lines
Point: Designates a location, has no size, named by a
capital letter
Line: Series of points that extends in 2 opposite direction
without end
Space: A set of all points.
Plane: Flat surface with no thickness; contains many lines
Collinear Points: Points that lie on the same line
Segment:
AB
Definition: Part of a line consisting of two endpoints and all
points in between. (Segment AB or BA)
How to sketch:
A
B
How to name: AB or BA
The symbol AB is read as "segment AB".
Ray:
AB
Definition: Part of a line consisting of one endpoint and all
the points of the line on one side of the endpoint.
When naming, endpoint must be listed first. (AB
and BA are not the same)
A
How to sketch: R
R
How to name: RA ( not AR )
RA or RY ( not RAY )
A
Y
( the symbol RA is read as “ray RA” )
Opposite Rays:
Definition: Two collinear rays with the same endpoint.
Opposite rays always form a line.
( Opposite rays must have the same “endpoint” )
X
A
Y
opposite rays
D
E
DE and ED are not opposite rays.
Naming Segments and Rays
Name the segments and rays in the figure.
A segment is a part of a line consisting of two endpoints and all
points between them. A segment is named by its two endpoints. So
the segments are BA (or AB) and BC (or CB).
A ray is a part of a line consisting of one endpoint and all the points
of the line on one side of that endpoint. A ray is named by its
endpoint first, followed by any other point on the ray. So the rays are
BA and BC.
Vocabulary (cont)
Parallel Lines:
AB CD
Definition: Coplanar lines that do not intersect
Skew lines:
Definition: Noncoplanar (they do not lie in the same flat surface),
therefore they are not parallel and do not intersect.
Parallel Planes:
Definition: Planes that do not intersect.
Plane KLQP II plane NMRS
Plane KLMN II plane PQRS
Plane PKNS II plane QLMR
Naming Parallel and Skew Lines
Use the figure below. Name all segments that are parallel to
AE. Name all segments that are skew to AE.
Parallel segments lie in the same plane, and the lines that contain
them do not intersect. The three segments in the figure above that
are parallel to AE are BF, CG, and DH.
Skew lines are lines that do not lie in the same plane. The four lines
in the figure that do not lie in the same plane as AE are BC, CD, FG,
and GH.
Vocabulary (cont)
A
Perpendicular Lines:
C
AB  CD
D
B
Definition: Lines which intersect to form a right angle (90°)
Midpoint:
Segment
A
AC
B
C
with midpoint B.
Definition: Divides a line segment into two congruent (equal) segments.
Intersect:
Definition: Crossing or sharing a point
A street map can be thought of as a series of parallel, intersecting,
and skew segments.
Name a street that is parallel to
Park Street.
Name a street that intersects
State Street.
Name a street that intersects
Hemlock Avenue.
Will a car traveling on Hill
Street ever meet a car
traveling on Crosstown
Road? Explain.
Name all streets on the
map that are parallel to
State Street.
Enrichment 1-3