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Circles and More Symmetry
Slideshow 38, MathematicsMr Richard Sasaki
Room 307
Objectives• Learn and recall the main properties of circles• Understand how to find lines of symmetry
about a pair of intersecting circles• Complete shapes about set lines of symmetry
and rotational symmetry
Note: Please bring a compass next lesson!
The Circle
CentreRadius
Tangent
DiameterChord
SectorRadii (plural of radius)
CentreCentral Angle
Arc Length
Answers
parallel90 tangents
perpendicular
sizes tangents
2
1A regular pentagon
No, it makes no difference.
Lines of SymmetryWhat is a line of symmetry?It is a line that shows reflection between two congruent sides of a shape.
Lines of symmetry always imply congruence on both sides.
Do congruent sides imply that there is a line of symmetry?Not necessarily. An example of this is the rectangle.This is not a line of symmetry.
Lines of SymmetryIf this was a line of symmetry, what shape would it be?A kite!
Try to remember…Lines of symmetry imply lines of congruence but lines of congruence do not imply lines of symmetry.
Let’s complete some shapes about their lines of symmetry!
Answers – Part 1
Answers – Part 2
Rotational SymmetryIf we know a shape’s order of rotational symmetry, we can draw it in its entirety!ExampleComplete the diagram so that the shape shown has rotational symmetry of order.
Order of Rotation 12
Answers
Order of Rotation 2
Answers
Order of Rotation 24
Answers
Order of Rotation 24
Answers
Order of Rotation 248