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Symmetry

by Steve Bishop, Lecturer at Further education on Dec 04, 2009

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SymmetryPresentation Transcript

• Symmetry
BTEOTSSSBAT solve problems involving rotational and reflection symmetry
• Key words
symmetry
reflection
rotation
• A shape is symmetrical if it contains some kind of repeating pattern.
There are two kinds of symmetry:
Reflectional symmetry and Rotational symmetry
A shape has rotational symmetry if you can turn the page round and the shape is the same when the page is a different way up.
A shape has reflectional symmetry if you can draw a mirror line through it so that the shape is the same on both sides of the line.
• B C
D
If the shape is rotated, then the shape will be the same 4 times with points B, C, D and back to A on top. We say it has rotational symmetry order 4.
Rotational symmetry
A
• Reflectional symmetry
If we look at a rectangular piece of paper we can fold it on the dotted lines and then each half of the shape will be identical. We say that it has two lines of symmetry. If a mirror were placed on these lines, then the reflections would be the same.
• Now try these
For each shape state the order of symmetry and then draw on the lines of symmetry.
• Plane symmetry
The ideas of symmetry can be applied to solid objects.
In this case however you find a plane of symmetry rather than a
line of symmetry (a plane is a flat surface).