6th Grade Math Textbook, Fundamentals

 &KDSWHU

9-2

Classify and Measure Angles

Objective To classify angles by angle measure • To describe the position of points in relation to

an angle • To use a right angle as a benchmark to estimate an angle measure • To use a protractor to

measure angles • To use a protractor and straightedge to draw an angle of a given measure

The man is boarding the bus on a wheelchair ramp.
What type of angle is the ramp’s angle of incline?

Angles are measured in. Angles are

classified according to their degree measures.

degrees

Remember:The measure of angle ABC

can be written as mABC.

MNO

180 

mMNO 360

reflex angle

NM

O

JKL

mJKL 180

straight angle

J KL

Exterior Interior

ABC

0 

mABC 90

acute angle

BC

A

DEF

mDEF 90

right angle

EF

D

GHI

90 

mGHI 180

obtuse angle

HI

G

The two rays of an angle divide a plane into three sets of points:

• points on the rays (sides or vertex of the angle)


• points—all points in the plane
  between the two rays


• points—all points in the plane
  not part of the angle or its interior

You can use the easily recognizable shape of a right angle as a benchmark

for identifying types of angles and estimating angle measures.

An angle of 70 is an acute angle. An angle of 120 is an obtuse angle.

The ramp’s angle of incline is less than 90 , so it is an acute angle.

exterior

interior