1. Section 12–5 Geometry PreAP, Revised ©2013 viet.dang@humble.k12.tx.us
Symmetry
Section 12–5
Geometry PreAP, Revised ©2013
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12–5: Symmetry

2. Symmetry
Symmetry is a transformation of the figure where the image coincides with the pre-image.
Line of Symmetry is a line that divides the figure into two congruent halves
Rotational Symmetry can be rotated around a point by a certain number of degrees so that the image ends up to be exactly the same as the pre-image.
Plane Symmetry is a three-dimensional figure has if a plane can divide the figure into two congruent reflected halves.
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12–5: Symmetry

3. Line Symmetry
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12–5: Symmetry

4. Example 1
For each figure find (one of) the line(s) of symmetry. Write the equation of the line of symmetry.
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12–5: Symmetry

5. Example 2
For each figure find (one of) the line(s) of symmetry. Identify the amount of lines of symmetry.
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12–5: Symmetry

6. Example 3
For each figure find (one of) the line(s) of symmetry. Write the equation of the line of symmetry.
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12–5: Symmetry

7. Your Turn
For each figure find (one of) the line(s) of symmetry. Write the equation of the line of symmetry and the amount of lines of symmetry.
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12–5: Symmetry

8. Rotational Symmetry
It is the smallest angle through which a figure can be rotated to coincide with itself. The number of times the figure coincides with itself as it rotates through 360° is called the order of the rotational symmetry.
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12–5: Symmetry

9. Example 4
Tell whether each figure has rotational symmetry. If so, give the angle of rotational symmetry.
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12–5: Symmetry

10. Example 4
Tell whether each figure has rotational symmetry. If so, give the angle of rotational symmetry.
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12–5: Symmetry

11. Example 5
Tell whether each figure has rotational symmetry. If so, give the angle of rotational symmetry.
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12–5: Symmetry

12. Your Turn
Tell whether each figure has rotational symmetry. If so, give the angle of rotational symmetry.
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12–5: Symmetry

13. Plane vs. Axis Symmetry
Plane symmetry is a plane can divide a figure into two congruent halves.
Symmetry About an Axis is where there is a line about which a figure can be rotated so that the image and preimage are identical.
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12–5: Symmetry

14. Plane Symmetry
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12–5: Symmetry

15. Axis Symmetry
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12–5: Symmetry

16. Example 6
Tell whether the figure has plane symmetry, symmetry about an axis, or neither.
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12–5: Symmetry

17. Example 7
Tell whether the figure has plane symmetry, symmetry about an axis, or neither.
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12–5: Symmetry

18. Your Turn
Tell whether the figure has plane symmetry, symmetry about an axis, or neither. Then, I want you to be prepared to defend your answer.
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12–5: Symmetry

19. Assignment
Page , all
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12–5: Symmetry