9.5 Angles and Triangles p.551

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9.5 Angles and Triangles p.551
.
D
.
E
F
Name the angle in five different ways.
DEF, FED, or E
Angle DEF, angle FED,
2
.
P
.
R
Q
Name the angle in five different ways.
PQR, RQP, or Q
Angle PQR, angle RQP,
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Classifying Angles p.553
An angle whose measure is 90o.
Right angle
An angle whose measure is 180o.
Straight angle
.
.
.
C
D
E
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An angle whose measure is
greater than 0o and less
than 90o.
Acute angle
An angle whose measure
is greater than 90o and less
than 180o.
Obtuse angle
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Classify the angles as right, straight, acute or
obtuse.
Right angle
.
.
.
Straight angle
C
D
E
Obtuse Angle
Acute angle
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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.
15o
45o
3.
2.
1.
72o
75o
45o
18o
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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.
38o
2. 157o
3. 90o
1.
23o
90o
142o
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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
E
D
G
H
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Types of Triangles p. 556

• Equilateral triangle -
• Isosceles triangle
• Scalene triangle

All sides are
the same length.
Two or more sides
are the same length.
All sides are of
different lengths.
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Types of Triangles p. 556

• Right triangle
• Obtuse triangle
• Acute triangle

One angle is a right angle.
One angle is an obtuse angle.
All three angles are acute.
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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
x 89o 180o
24o
x
x 180o 89o
C
A
x 91o