GeomPHM5e_DNG_002-024
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Lesson 1-3 (pp. 17–24)
Segments, Rays, Parallel Lines, and Planes
Lesson Objectives 1 Identify segments and rays 2 Recognize parallel lines
NAEP 2005 Strand: Geometry Topic: Relationships Among Geometric Figures Local Standards: ____________________________________
Vocabulary. Segment AB AB
B
A Endpoint
A ray is
Ray YX
)
YX
Opposite rays are
Y Endpoint
X
Q
R and
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A segment is
S are opposite rays.
Skew lines are
C
D
H E
← →
AB is
←→
B
A
←→
to EF. ← →
AB and CG are
lines.
G F
Parallel planes are G A J D
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Lesson 1-3
H B
Plane ABCD is
to plane GHIJ.
I C
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Parallel lines are
GeomPHM5e_DNG_002-024
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Examples. 1 Naming Segments and Rays Name the segments and rays in the figure.
A
The labeled points in the figure are A, B, and C.
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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 and . B 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 and .
2 Identifying Parallel and Skew Segments Use the figure at right.
C
D
Name all segments that are parallel to AE. Name all segments that are skew to AE.
C B
A
Parallel segments lie in the same plane, and the lines that contain them do not intersect. The three segments in the figure that are parallel to , and . AE are
H E
G F
Skew segments are segments that do not lie in the same plane. The four segments in the figure that do not lie in the same plane as AE are
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,
and
,
.
3 Identifying Parallel Planes Identify a pair of parallel planes in your classroom. Planes are parallel if they are vertical,
. If the walls of your classroom walls are parts of parallel planes. If the ceiling and
floor of the classroom are level, they are parts of parallel planes.
Check Understanding.
)
)
1. Critical Thinking Use the figure in Example 1. CB and BC form a line. Are they opposite rays? Explain.
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Lesson 1-3
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GeomPHM5e_DNG_002-024
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Name_____________________________________ Class____________________________ Date________________
2. Use the diagram in Example 2. a. Name all labeled segments that are parallel to GF.
b. Name all labeled segments that are skew to GF.
3. Use the diagram to the right. a. Name three pairs of parallel planes.
S
Q R
P W T
V U
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* )
b. Name a line that is parallel to PQ .
c. Name a line that is parallel to plane QRUV.
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Lesson 1-3
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c. Name another pair of parallel segments and another pair of skew segments.
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