1-4 Segments, Rays, Parallel Lines, and Planes
Objectives:
• Define line segments and rays
• Properly name line segments and rays
• Identify parallel lines and skew lines
1
Line Segments
A
B
• A line segment is part of a line containing
two endpoints and all points between them.
• Unlike lines, which extend forever in both
directions, line segments have a definite
beginning and end
• A line segment is named with the endpoints
AB or BA
2
Rays
B
A
• A ray is part of a line that consists of one endpoint and
all points of the line extending in one direction
• Name a ray using the endpoint first and then another
point on the ray
– When naming, make sure the arrow points away from the
endpoint.
AB
, not BA
3
Rays, continued
B
AB
A
B
A
BA
• Are these two rays the same?
No
• Different endpoints
• Extend in different directions
4
Opposite Rays
J
K
L
• Are two collinear rays with the same
endpoint
• Always form a line
KJ and KL are opposite rays
5
Parallel Lines
• Lines that
– Never intersect
– Extend in the same directions
– Coplanar
6
Skew lines
Lines that:
• Never intersect
• Are noncoplanar
• Extend in different directions
7
Parallel Planes
• Parallel planes are planes that never
intersect
– Example: the purple planes in the above
illustration
• A line and plane that never intersect are
also parallel
8
Learning Check and Summary
• Which of the following has no endpoints?
– Ray, Line Segment, Line
• Which of the following has two endpoints?
– Ray, Line Segment, Line
• Which of the following has one endpoint and
extends in one direction?
– Ray, Line Segment, Line
• Which of the following extend in the same
direction?
– Parallel lines, skew lines
• Which of the following extend in different
directions?
– Parallel lines, skew lines
9
Exercises
• P. 13-15 All
• P. 253 All
• P. 255 All
10