9.5 Angles and Triangles p.551

..

D

EF

Name the angle in five different ways.

Angle DEF, angle FED, DEF, FED, or E

..

Name the angle in five different ways.

Angle PQR, angle RQP, PQR, RQP, or Q

P

Q R

Classifying Angles p.553

An angle whose measure is 90o.

An angle whose measure is 180o.

. . .C D E

Right angle:

Straight angle:

An angle whose measure is greater than 0o and less than 90o.

An angle whose measure is greater than 90o and less than 180o.

Acute angle:

Obtuse angle:

Classify the angles as right, straight, acute or obtuse.

. . .C D E

Straight angleRight angle

Acute angle

Obtuse Angle

Complementary Angles p. 554Two 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.

18o

2.75o

3.45o72o

15o 45o

Supplementary Angles p. 555Two 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.

1. 38o 2. 157o 3. 90o

142o 23o 90o

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.

A B

C

D E

F

G H

I

Types of Triangles p. 556

Equilateral triangle -

Isosceles triangle –

Scalene triangle –

All sides are the samelength.

Two or more sides are the same length.

All sides are of different lengths.

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.

Sum of the Angle Measures of a Triangle

In any triangle ABC, the sum of the measures

of the angles is 180o.

A

B

C

65o

24o

Find the measure of angle A.

x + 65o + 24o = 180o

x + 89o = 180o

x = 180o – 89o

x = 91o

x