U2 L4 Symmetry Lesson.notebook 1 October 23, 2017 Oct 54:54 PM U2 L4 Symmetry Oct 54:55 PM Line or Reflectional Symmetry A figure is a reflection symmetric figure if and only if there exists a line such that the figure and its image COINCIDE when the figure is reflected in that line. The line is called the SYMMETRY LINE for the figure. A figure may have more than 1 symmetry line.
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U2 L4 Symmetry Lesson.notebook
1
October 23, 2017
Oct 54:54 PM
U2 L4
Symmetry
Oct 54:55 PM
Line or Reflectional Symmetry
A figure is a reflection symmetric figure if and only if there exists a line such that the figure and its image COINCIDE when the figure is reflected in that line.
The line is called the SYMMETRY LINE for the figure. A figure may have more than 1 symmetry line.
U2 L4 Symmetry Lesson.notebook
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October 23, 2017
Oct 55:07 PM
Symmetrical Figures
Non-Symmetrical Figures
Oct 55:18 PM
Many familiar shapes have symmetry lines, but not always every line you might think.
The rectangle does have 2 symmetry lines, but not its diagonals.
Draw a rectangle and its 2 symmetry lines.
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Can you draw a regular hexagon and sketch its symmetry lines.
Oct 172:40 PM
Rotational Symmetry
Rotational Symmetry when a figure can be mapped onto itself by a rotation of 180 degrees or less
B C
D
A'A'
B'
C'
D'D'A
B'
C'
45 degree rotation 90 degree rotation
A rotation of 0 or 360 is considered an identity rotation because every figure has 0 and 360 rotational symmetry.
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Oct 55:44 PM
Order of Rotational SymmetryThe number of positions in which the figure coincides with the preimage when rotating.
Order = 1 is for all figures, and is why we don't use 0 or 360 degrees for rotational symmetry.
Find the order of of rotational symmetry for each.
360/120=3The order is 3!
Don't worry about this concept. I'll mention it, if we have time...
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Oct 55:50 PM
Figures with no rotational symmetry
Oct 55:52 PM
Point Symmetry
or 180 Rotational Symmetry
Turn the figure upside down (rotate it 180 degrees), and if the image will coincide with the preimage, then it has Point Symmetry.
Every point on a figure with Point Symmetry has a matching point on the figure that is the same distance from the center (rotation) point but in the opposite direction.
Point Symmetry when a figure can be mapped onto itself by a rotation of 180 degrees.
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Oct 510:2P
Examples of figures with Point Symmetry
Can you think of some more?
Every figure with point symmetry has order > 2.
Oct 510:24 PM
U2 L4
Symmetry
homework
online
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October 23, 2017
Oct 2310:27 AM
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