Page 90 - Maths Skill - 6

88 Maths

Let the two rays be OA and OB with the same initial point ‘O’ .

Then O is called the vertex of the angle and rays OA and OB are called arms of the angle.

Notation for an Angle

We use the symbol ∠ for naming an angle. So the angle in Fig.6.8 can be named as
∠AOB or ∠BOA. Fig. 6.8

DEGREE MEASURE OF AN ANGLE
On the basis of numerical values, it will be easy to know how much one angle is bigger or smaller than the other.
For this, we measure an angle in terms of some standard unit of measurement known as degree of an angle.

Consider a ray OA as shown in Fig. 6.9 (i), O is the vertex, start rotating in the anticlockwise direction about O.
When the ray OA takes one full turn as shown in Fig. 6.9 (vi), it describes an angle known as complete angle. The
complete turn or circle is divided into 360 equal parts. Each part measures one degree. The symbol ‘°’ is used to
denote degrees.

(i) (ii) (iii)

(iv) (v) (vi)

Fig. 6.9

For example; 1 degree is written as 1°. 22 degree is written as 22° and 75 degree is written as 75°, etc.

Fact-o-meter

A degree is further divided into 60 equal sub-parts, each part is called a minute. It is
denoted by the symbol (′), i.e., 1° = 60′.
For example; 1 minute = 1′ ; 15 minutes = 15′, etc.
If we further divide a minute into 60 equal sub-parts, then each part is called a second. It
is denoted by the symbol (″), i.e., 1′ = 60″.
For example; 1 second = 1″ ; 18 seconds = 18″, etc.