Page 54 - Mathematics Coursebook

5 Angles

When you measure lengths you use di!erent units, including Key words
Key words
Key words
millimetres, metres and kilometres. But length is not the only type
of measurement you need to make when you are looking at "at Make sure you learn and

shapes. Sometimes, you need to change direction, for example, if understand these key words:
you turn a corner. angle
A turn between one direction and another is called an angle. You degree
measure angles in degrees. One whole turn is 360 degrees, written right angle
as 360°. acute angle
Humans have needed to measure angles for a long time. When obtuse angle
line segment
early astronomers looked at stars in the sky, they wanted to reflex angle

describe their positions relative to one another. $e natural way to protractor
do this was to use angles. We know that the ancient Babylonians equilateral
and Egyptians divided a whole turn into 360 parts, as long ago as quadrilateral
1500 BC. vertically opposite angles

perpendicular
Why are there 360 degrees in a whole turn? parallel
A clay tablet excavated in Shush, in what is now modern-day Iran, transversal
shows that Babylonians divided a whole turn into 360 units. One isosceles
reason could be that many simple fractions of a whole turn of 360°,

1 1 1 1
1
including ,, , and , can be written as a whole number of
2 3 4 5 6
degrees. It may also be because there are approximately
360 days in a year.
The angles of a triangle

$e sum or total of the angles of a triangle is always 180°.

In this unit you will learn about other angle facts and use them to
solve problems.

Ancient Babylonian tablet
recording measurements.

5 Angles 53