Page 125 - Math Smart - 7

In this chapter
CHAPTER 6.1
Pupils should be able to:
• identify, describe and

Types of Angles estimate the size of
angles and classify them
as acute, right or obtuse

6.1.1 Naming angles • identify, describe and
estimate the size of
angles and classify angles
An angle is formed when two line segments share the same vertex (corner). The as reflex
line segments form the arms of the angle.

Angles are measured in degrees. An angle measures the amount of turn. We use a
protractor to measure the amount of turn of an arm from its original position.
We use the letters of the alphabet to label angles. Capital letters are used at the
ends of the arms of the angle, and at the vertex of the angle. vertex <;angle
In Figure 6.1, the letters A, B, C and 0 are used. The letter O is the vertex of the
angles.

In the diagram
• the lines OA, OB and OC make up the arms of the angles. The lines are:
OA, OB and OC

• there are three angles namely AOB, BOC and AOC.
The symbol (") is used to show which letter is the vertex of the angle.

Lower-case letters can also be used to name the angle.
For example, ^a, /.band Ac. Notice that Ac= Aa+ Ah
s Figure 6.1

1.2 Types of angles ^ RECALL

In Stage 5, we learnt to identify acute, right and obtuse angles, and a straight
Write down the
line. We will now learn about reflex angles and a revolution.
measurements of the
angles below.

An acute angle measures A right angle is equal An obtuse angle
between 0® and 90°. to 90°. measures between
90° and 180°.

A straight line is
equal to 180°
A reflex angle measures A revolution
between 180° and 360° is equal to 360°