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1.4 Angles & Their Measures (Page 1 of 2)
Angle
two different rays that have the same initial point
The rays are the sides of the angle.
The initial point is called the vertex of the angle.
Angles are classified as acute, right, obtuse, and straight.
Adjacent s
two angles that share a common vertex and one side but
have no common interior points
Congruent s angles that have the same measure
MEASURES ARE EQUAL
mBAC
=
mDEF
The measure of angle BAC is equal to
the measure of angle DEF.
ANGLES ARE CONGRUENT
BAC
 DEF
Angle BAC is congruent to
angle DEF.
P3) Protractor P
 Rays can be matched one to one with the real numbers
from 0 to 180.
 The measure of a ray is equal to the absolute value of the
difference between the real numbers for OA and OB.
1.4 Angles & Their Measures (Page 2 of 2)
A
D
P4) Angle + P (Postulate)
B
C
 If D is in the interior of ABC,
then ABD + DBC = ABC.
 Interior and exterior areas are created.
 Adjacent angles are created.
Angle Classification
Acute s
angles that measure greater than 0 o but less than 90 o
Right s
angles that measure 90 o
Obtuse s
angles that measure greater than 90 o but less than 180 o
Straight s
angles that measure 180 o