Sec 1-4
Concepts: Classifying Angles
Objectives: Given an angle, name, measure and classify it as
measured by a s.g.
Example 1: Name the <‘s in the figure
H
S
1
O
2
G
<HOS
<SOH
<1
<SOG
<GOS
<2
<HOG
<GOH
Classify the angle with the given measure
as acute, obtuse, right or straight.
m<T = 90
right
m<X = 180
straight
m<Y = 32
acute
m<A = 160
obtuse
Use a protractor to measure
the angle. Then classify it.
2.
1.
101
131
Example 3: Find the indicated
angle measure
a
d
120
b
c
15
60
g
f
e
Example 4: For each city on the polar map, estimate
the measure of <BOA where B is on the Prime Meridian
(0۫ Longitude), O is the North Pole and A is the City
Clyde River, Canada
About 69
Reytjavik Iceland
About 21
Fairbanks Alaska
About 148
Old Crow Canada
Angmagssalik Greenland
Tuktoyaktuk, Cananda
About 38
About 140
About 133
Angle Addition Postulate
If P is in the interior of <RST,
then m<RSP +m<PST = m<RST
R
Example 5:Find the
m<RST
50° P
60°
S
T
50 + 60 = 110°
Example 6: Use the angle addition
postulate to solve for x. Then find the
measure of each angle.
A.
P
O
Q
(X+4) + (2x-2) = 26
3x+2=26
R
3x=24
X=8
m<POQ = 8+4 = 12
m<QOR = 2(8)-2= 14
m<POR = 26
Example 6 cont.: Use the angle addition
postulate to solve for x. Then find the
measure of each angle.
B. P
O
(3X+7) + (5x-2) = 61
Q
8x+5=56
R
8x=56
X=7
m<POQ = 3(7)+7 = 28
m<QOR = 5(7)-2=33
m<POR = 61
Example 7: JK bisects < HJL. Given that
m<HJL=42°, what are the measures of
<HJK and <KJL?
42
H
K
m<HJK and
m<KJL must each
be half of 42.
J
L
m<HJK and
m<KJL = 21
Example 8: BD bisects <ABC.
Find the value of x.
A
5x+5 = 6x-2
(5x+5) D
(6x-2)
B
-5x
-5x
5=x-2
C
Since BD bisects <ABC,
then m<ABD = m<BDC
+2 +2
7=x
Today’s Work