How_To_Be_Good_At_Math

258 GEOMETRY •^ ROTATIONAL SYMMETRY

Rotational symmetry

We say that an object or shape has rotational symmetry if it can be

turned, or rotated, about a point until it fits exactly into its original outline.

Symmetrical

or not?

Three of these

flower shapes have

rotational symmetry.

Can you spot the

one that doesn’t?

TRY IT OUT

Answer on page 320

Centre of rotational symmetry

The point about which an object is rotated is

called its centre of rotational symmetry.

We can rotate the

object so it fits into

its original outline

If we rotate the rectangle around the pin, after

half a turn it will fit exactly over the outline we

drew. This means it has rotational symmetry.

Another half turn will bring the rectangle back to its

starting position.

Let’s take a rectangular piece of card and put

a pin through its centre, which is the point

where the rectangle’s two diagonals meet. Now

let’s draw around the outline of the rectangle.

Draw pencil lines

from opposite corners

to find the centre

Centre of rotational

symmetry

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