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3.1 Identify Pairs of Lines and Angles
Parallel Lines
• Coplanar
• Do not intersect
• Segments and rays are parallel if they lie on parallel lines.
CDAB ||
A
D
C
B
Triangles, like those above in red, indicate that 2 lines are parallel.
Parallel planesif they never intersect
A D
E H
G
CB
F
? Dcontains and AB toParallel
CD�������������� �
AD
E H
G
CB
F
? Dcontains and AB lar toPerpendicu
AD�������������� �
Skew Lines: Do not intersect, but do not lie in the same plane.
A D
E H
G
CB is skew to AE BC
���������������������������������������� ���
skew ?GH�������������� �
skew ?EH�������������� �
A D
E H
G
CB
F
? Dcontains and AB Skew to
DH�������������� �
,DF etc�������������� �
A D
E H
G
CB
F
ABE plane toparallel be toappears and
Dcontain that plane(s) theName
plane DCG
#13: Parallel PostulateParallel Postulate
If there is a line and a point not on the line,
#13: Parallel PostulateParallel Postulate
If there is a line and a point not on the line, then there is exactly one line through the point and parallel to the line
#14: Perpendicular PostulatePerpendicular Postulate
If there is a line and a point not on the line, then there is exactly one line through the point and perpendicular to the line
Transversal; intersects 2 or more coplanar lines
4 and 2 3 and 1 6 and 8
5 and 7
Corresponding Angles
Same side of transversalCorresponding position
8 and 4 5 and 1
Alternate Exterior Angles“Alternate” opposite sides of
transversal“Exterior” outside of the two lines
3 and 7 2 and 6
Alternate Interior Angles“Alternate” opposite sides of
transversal“Interior” inside of the two lines
3 and 2 6 and 7
Consecutive Interior Angles“Consecutive” “together”; same side
of the transversal“Interior” inside of the two lines
A#20:A#20:
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