Page 2 - CH - 2 - LN- 2.3

 Straight Angle: A straight angle is half of a full turn. Since a full turn is 360°, a straight angle
is 180°.

 Right Angle: Two right angles together make a straight angle. Since a straight angle is 180°, a
right angle is 90°.

For example, if you look at the hands of a clock, the angle between them at different times can be
measured in degrees. At 3 o'clock, the angle between the hour and minute hands is a right angle
(90°).

Why 360 Degrees?

But why 360°? The exact reason is a bit of a mystery, but there are several historical reasons:

 Ancient civilizations, like those in India, Persia, Babylon, and Egypt, used a year with 360 days
in their calendars.
 The number 360 is practical because it can be divided evenly by many numbers (like 1, 2, 3,
4, 5, 6, 8, 9, 10, and 12), making it easier to split a circle into equal parts.

This divisibility is why 360° has been used for so long—it’s just really convenient!

Degree Measures of Angles
Measuring angles is a fundamental concept in geometry, and to do this accurately, we use a tool
called a protractor. A protractor is either a full circle divided into 360 equal parts or a half-circle
divided into 180 equal parts.

Using a Protractor
 Protractor Structure: A typical protractor has a straight angle at the center, divided into 180
units of 1 degree each. These units help you measure angles precisely.