1. An angle is formed by two rays that share a common endpoint called the vertex. Angles can be named using symbols like ∠XYZ or a number like ∠5. 2. Angle measures are reported in degrees (°) as measured using a protractor. Angles with the same measure are congruent. 3. The measure of an angle is the absolute value of the difference between the two numbers the angle rays align with on a protractor. Interior angles are inside the angle lines, exterior are outside, and an angle on a line is on the angle.

1. 1.4 Angles & their Measures
p. 26

2. Angle symbol: ∠
• 2 rays that share the same endpoint (or
initial point)
Sides – the rays XY & XZ
Y
5 X
Z
Vertex – the common
endpoint; X
Named <YXZ, <ZXY (vertex is
always in the middle), or <X (if Angles can also be
it’s the only <X in the diagram). named by a #. (<5)

3. There are 3 different <B’s in this diagram;
therefore, none of them should be called <B.
A
<B ? D
B
C

4. Angle Measurement
• m<A means the • Angles with the
“measure of <A” same measure are
• Measure angles with congruent angles.
a protractor. • If m<A = m<B,
• Units of angle then <A ≅ <B.
measurement are
degrees (o).

5. Postulate 3: Protractor Post.
• The rays of an angle
55o
can be matched up
with real #s (from 1 to 20o
180) on a protractor
so that the measure
of the < equals the
absolute value of the
difference of the 2 #s. m<A = 55-20
= 35o

6. Interior or Exterior?
• B is ___________
in the interior
• C is ___________
in the exterior
on the <
• D is ___________
B
C
D
A

7. Post. 4: Angle Addition post.
• If P is in the interior of <RST,
then m<QRP + m<PRS = m<QRS.
If m<QRP=5xo,
m<PRS=2xo, &
P S m<QRS=84o, find x.
5x+2x=84
Q
7x=84
x=12
m<QRP=60o m<PRS=24o
R

8. Types of Angles
• Acute angle – Measures between 0o & 90o
• Right angle – Measures exactly 90o
• Obtuse angle – Measures between 90o & 180o
• Straight angle – Measures exactly 180o

9. Adjacent Angles
• 2 angles that share a common vertex &
side, but have no common interior parts.
(they have the same vertex, but don’t
overlap) such as <1 & <2
2
1

10. Example:
• Name an acute angle
<3, <2, <SBT, or <TBC
S
• Name an obtuse angle
T
<ABT
3
• Name a right angle 1
2
<1, <ABS, or <SBC A B C
• Name a straight angle
<ABC

11. Assignment