# Angles and Triangles p.551 D E F

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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 R Q Name the angle in five different ways. Angle PQR, angle RQP,
PQR, RQP, or Q

. . . Classifying Angles p.553 Right angle:
An angle whose measure is 90o. Straight angle: An angle whose measure is 180o. . . . 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.
Right angle . . . Straight angle C D E Obtuse Angle Acute 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. 15o 45o 2. 3. 1. 72o 75o 45o 18o

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. 1. 38o o 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. I C F A B E D G H

Types of Triangles p. 556 All sides are the same length.
Equilateral triangle - Isosceles triangle – Scalene triangle – 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. Find the measure of angle A. B x + 65o + 24o = 180o 65o x + 89o = 180o x 24o x = 180o – 89o C A x = 91o