How_To_Be_Good_At_Math

230 GEOMETRY •^ ANGLES

Angles

An angle is a measure of an amount of turn, or rotation,

from one direction to another. It is also the difference in

direction between two lines meeting at a point.

Describing angles

An angle is made of three parts:

two lines, called arms, and a

vertex, where the arms meet.

We show the angle by drawing

a curved line, or arc, between

the arms. The size of the angle is

written inside or next to the arc.

Let's look at some

lines turning round a

centre point. As they turn,

they create angles.

One end of the

green line has

stayed still at the

centre, while the

other end has

started to turn.

If the purple

line turns to

here, it has turned

one quarter of

the way from

where it started.

We call this a

quarter turn.

If we keep

turning the

line round the

centre, it will arrive

back where it started

from, like the red line.

This is a full turn.

Lines begin turning

from here

The blue line has turned

half way round from

where it started, making a

straight line. We call this a

half turn.

Vertex

Angle

Arm

Arm

An angle is a measure

of the amount that

something has turned

around a fixed point.

30º

Centre

230_231_What_is_an_Angle.indd 230 29/02/2016 18:05