Measure and Classify
Angles
1.4 Geometry
Angles
An angle is created by two rays that
have a common endpoint
Each ray is called the side of the angle. The common
endpoint is called the vertex of the angle. The amount
of rotation about the vertex is called the measure of the angle.
Common units of measurement of angles are degrees and
radians.
C
A
B
Parts of an angle
C
Exterior of angle
Interior of angle
A
B
Angles are written with either
the vertex point [if no other
angles share this vertex] or a
point on one of the rays, the
vertex, and the point on the
other ray.
A
CAB
BAC
Types of angles
Acute
 Obtuse
 Right
 Straight

0o < acute < 90o
 90o < obtuse < 180o
 right = 90o
 Straight = 180o

Adjacent angles
C
D
O
A
DOC is adjacent to COA
DOA is NOT adjacent to COA
Protractor Postulate

Each rotation of a ray about a vertex has a
unique value between 0 and 180 degrees
Angle Addition Postulate
C
D
O
A
If C is in the interior of AOD, then
mAOC + mCOD = mAOD
Angle measures
mFAB = 90
mEAB = 60
mBAG = 120
mDAB = 45
mBAH = 135
G
mBAI = 150
F
H
D
I
mBAJ = 180
J
mBAC = 30
E
C
A
B