How_To_Be_Good_At_Math

212 GEOMETRY • 2D SHAPES

2D shapes

2D shapes are flat, like the shapes we draw on

paper or on a computer screen. 2D is short for two-

dimensional, because the shapes have length and

height, or length and width, but no thickness.

Describing a

polygon

We usually mark the

sides of a polygon with

dashes to show which

sides are the same

length as each other.

All sides are marked

with one dash to

show they are equal

Vertex

Vertex

Side

Side

Non-polygons

Other 2D shapes can be made

from curved lines, like this circle, or by

a combination of straight and curved

lines, like the shape next to it.

Naming polygons

Polygons are straight-sided shapes

made of three or more sides and angles.

Angles are made by two lines meeting at

Angles at a point

To show that all the sides

are the same length, each

side of this six-sided shape

(hexagon) is marked with a

single dash.

This hexagon has three sets of sides

of the same length. The first pair is

marked with one dash, the second pair

with two dashes, and the third pair with

three dashes.

The sides with

one dash are the

same length

Polygons and non-polygons

The sides with

two dashes are

the same length

212_213_2D_shape_Regular_irregular_polygons.indd 212 29/02/2016 18:04