Page 96 - Revised Maths Wisdom Class - 6

94 MATHS

(d) (e) (f)

Angles
Look at the pictures given below of some physical objects that we often encounter in our day-to-day life.

Clock Divider Scissors Forceps
Fig. (a)

Here, we could notice one common thing that both the arms of each picture are
hinged at a point, such that they are inclined towards each other and have an
opening between them. Thus, we can say that these arms form an angle at a point
of their joint.

An angle is a figure formed by two different rays starting from the same initial
point. The common starting point of the two rays is called vertex of the angle and
the two rays are known as its arms or sides as shown in Fig. (b). Fig. (b)

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.(c) can be named
as ∠AOB or ∠BOA.

Fig. (c)
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. (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. (vi), it describes an angle known as complete angle. The complete