Section 3.1
Exploring Lines and Planes
Parallel Lines
• Are coplanar lines that do not intersect.
• Parallel Lines have the same slope.
• Intersecting Lines- are coplanar and have exactly one
point in common. If they meet at right angles, they are
perpendicular otherwise they are oblique
Theorem 3.1
Transitivity of Parallel Lines- if two lines are parallel to the
same line, then they are parallel to each other.
Theorem 3.2
• Property of Perpendicular Lines- if two coplanar lines are
perpendicular to the same line, then they are parallel to
each other.
• Remember that perpendicular lines have slopes that are
negative reciprocals
Skew Lines
• Are two lines that do not lie in same plane.
• They do not intersect and are not parallel
B
C
D
A
G
E
F
Planes
• Parallel planes are two planes that do not intersect.
• EX: floor and ceiling of most rooms are parallel.
• Sketch:
1. Two planes that intersect but are not perpendicular.
2. Two parallel planes, each perpendicular to a third plane.