Page 152 - Math Skill - 5

150 Maths

™ Area bounded by the arms is said to form the interior C
of an angle.
O
™ Area outside the arms forms the exterior of an angle.
Exterior M
™ Points M and N are in the interior of the angle CAB
and points O and P are in the exterior of the angle CAB. Interior N
A B
Comparison of Angles P

We can compare two given angles by tracing paper as explained in the following example.

Let’s Attempt

Example: Compare the angles ∠PAQ and ∠LOR as given below.

R
Q

O

A
P L R
Solution: Trace ∠LOR on a paper. Place the tracing of ∠LOR on Q

∠PAQ such that O falls on A and OL falls along AP .

Since, AQ falls in the interior of ∠LOR

So, ∠LOR > ∠PAQ O(A) L(P)

Measuring Angles

We measure angles in degrees. The symbol for degree is ‘°’. A complete turn around a point
is divided into 360 equal parts. Each of these parts is called a
degree and is denoted by 1°. We use a special geometrical tool
to measure angles called protractor.

It looks like as shown below.
The protractor is in the shape of a semi-circle and the midpoint
of its horizontal edge or base line is called its centre. A protractor
has two scales—inner and outer. One scale begins with 0° on the Centre base line
right and moves to 180° on the left. The other scale starts with 0° on the left and moves to 180°
on the right. The smallest division on a protractor is equal to 1°.
To measure an angle ∠ABC using protractor, we follow these steps:
C
Step 1: To measure ∠ABC, place the protractor in such a way that its

centre lies on B and the arm BA coincides with the horizontal

edge or base line of the protractor. B
A