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1.5 – Angle Relationships
KEY CONCEPT – Adjacent Angles
Words Adjacent angles are two angles that lie in the same plane, have a
common vertex and a common side, but no common interior
points.
Example
Nonexamples
ABC and CBD
ABC and ABD
ABC and BCD
Example 1 – Name two acute adjacent angles.
KEY CONCEPT – Vertical Angles
Words Vertical angles are two nonadjacent angles formed by two
intersecting lines. Vertical angles are congruent.
Example
Nonexamples
AEB and CED
AED and BEC
AED and BEC
Example 2 – Refer to the figure in Example 1. Name two acute vertical
angles.
KEY CONCEPT – Linear Pair
Words A linear pair is a pair of adjacent angles with noncommon sides
that are opposite rays.
Example
Nonexamples
DEB and BEC
DEB and BEC
Example 3 – Refer to the figure in Example 1. Name two angles that form a
linear pair.
KEY CONCEPT – Complementary Angles
Words
Complementary angles are two angles with measures that
have a sum of 90.
Examples
1 and 2 are complementary.
PQR and XYZ are complementary.
Example 4 – Find x.
9 x
6 x
KEY CONCEPT – Supplementary Angles
Words
Supplementary angles are two angles with measures that have
a sum of 180.
Examples
EFH and HFG are supplementary.
M and N are supplementary.
Example 5 – Find y.
11y  12 
L6 – pg 45 (8-14 & 16)
69