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9.5 Angles and Triangles p.551
.
D
E
.F
Name the angle in five different ways.
Angle DEF, angle FED, DEF, FED, or E
.
P
Q
.R
Name the angle in five different ways.
Angle PQR, angle RQP,
PQR, RQP, or Q
Classifying Angles p.553
o
Right angle: An angle whose measure is 90 .
o
Straight angle: An angle whose measure is 180 .
. . .
C
D
E
Acute angle: An angle whose measure is greater
than 0o and less than 90o.
Obtuse angle: An angle whose measure is
greater than 90o and less than 180o.
Classify the angles as right, straight,
acute or obtuse.
. . .
Straight angle
C
D
E
Obtuse Angle
Acute angle
Right angle
Complementary Angles p. 554
Two angles are complementary if the sum
of their measures is 90o. Each angle is
called a complement of the other.
Find the measure of a complement of the angle.
1.
2.
o
72
18o
o
15
75o
o
3. 45
45o
Supplementary Angles p. 555
Two angles are supplementary if the sum
of their measures is 180o. Each angle is
called a supplement of the other.
Find the supplement of the angle given.
o
1. 38
o
142
o
2. 157
o
23
3. 90o
o
90
Triangles p. 555
A triangle is a polygon made up of three
segments, or sides. A triangle with vertices A,
B, and C can be named ABC.
I
C
F
A
B
D
E
G
H
Types of Triangles p. 556
Equilateral triangle - All sides are the same
length.
Isosceles triangle – Two or more sides are the
same length.
Scalene triangle – All sides are of different
lengths.
Types of Triangles p. 556
Right triangle – One angle is a right angle.
Obtuse triangle – One angle is an obtuse angle.
Acute triangle – All three angles are acute.
Sum of the Angle Measures of a Triangle
In any triangle ABC, the sum of the measures
of the angles is 180o.
Find the measure of angle A.
B
x + 65o + 24o = 180o
65o
A
x
o
o
x + 89 = 180
o
24
o
o
x
=
180
–
89
C
o
x = 91
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