Page 1 - LN 7
P. 1
Subject – Mathematics
Chapter 7 – GEOMETRY
Sub-topic 7 : Construction of angles using protractor.
Measuring Angles
The size of an angle is usually measured in degrees (°). Think of a circle which is divided into 360
equal sectors. Each sector has a small angle at the centre of the circle – the size of such angle is 1
degree (written: 1°). In other words, the size of an angle is a measure of how wide the angle is at the
vertex bound by the two sides.
Given an angle ABC,
How do we measure the size of the angle? We can measure angles using an instrument known as
a protractor.
What is a protractor?
A protractor is an instrument used to measure the size of angles.
The protractor shown below has two scales:
The outer scale starts from 0˚ to180˚ going clockwise.
The inner scale starts from 0˚ to 180˚ going anti-clockwise.
