Page 646 - Basic College Mathematics with Early Integers

S E C T ION 9 .1 I LINES AND ANGLES 623

Objective Classifying Angles as Acute, Right,
Obtuse, or Straight

An angle can be measured in degrees. The symbol for degrees is a small, raised
circle, °.There are 360° in a full revolution, or a full circle.
360

1 1
of a revolution measures (360°) = 180°. An angle that measures 180° is
2 2
called a straight angle.

180

R S T
RST is a straight angle.
1 1
of a revolution measures (360°) = 90°. An angle that measures 90° is called
4 4
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.

40
62

Acute angles
An angle whose measure is between 90° and 180° is called an obtuse angle.

95
PRACTICE 3
120
Classify each angle as acute,
Obtuse angles right, obtuse, or straight.
a. b.
Example 3 Classify each angle as acute, right, obtuse, or straight. N
R
a. b.

c. d.
S
R
M
Q
c. d.

Answers
Q 3. a. obtuse b. straight c. acute
T Continued on next page d. right