1. 1.4 Angles & their Measures
p. 26

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

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

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

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

6. Interior or Exterior? B is ___________ C is ___________
D is ___________
in the interior
in the exterior
on the < 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, & m<QRS=84o, find x.
5x+2x=84
7x=84
x=12
m<QRP=60o m<PRS=24o S P Q R

8. Types of Angles Acute angle – Right angle – Obtuse angle –
Straight angle –
Measures between 0o & 90o
Measures exactly 90o
Measures between 90o & 180o
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
Name an obtuse angle
<ABT
Name a right angle
<1, <ABS, or <SBC
Name a straight angle
<ABC S T 3 1 2 A B C

11. Assignment