Page 703 - Basic College Mathematics with Early Integers

680 C HAPTE R 9 I GEOMETRY

Definitions and Concepts Examples

Section 9.1 Lines and Angles (continued)

A line segment is a piece of a line with two endpoints.
A B
Line segment AB or AB
A ray is a part of a line with one endpoint. A ray extends
A B
indefinitely in one direction. ¡
Ray AB or AB
A
An angle is made up of two rays that share the same
B
endpoint.The common endpoint is called the vertex.
Vertex C
An angle that measures 180° is called a straight angle. 180

R S T
∠ RST is a straight angle.
An angle that measures 90° is called a right angle. The
symbol is used to denote a right angle.
A

B C
∠ ABC is a right angle.
An angle whose measure is between 0° and 90° is called an
acute angle.
45
62
Acute angles

An angle whose measure is between 90° and 180° is called 120 95
an obtuse angle.
Obtuse angles

Two angles that have a sum of 90° are called complementary
60
angles. We say that each angle is the complement of 30
R S
the other. Complementary angles
60 30 90

Two angles that have a sum of 180° are called 125
supplementary angles. We say that each angle is the 55
supplement of the other. M N
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Supplementary angles
125 55 180