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Isometry - PowerPoint PPT Presentation


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To transform something is to change it. In geometry, there are specific ways to describe how a figure is changed. The transformations you will learn about include: Translation Rotation Reflection Dilation. Isometry.

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Isometry


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    1. To transform something is to change it. In geometry, there are specific ways to describe how a figure is changed. The transformations you will learn about include: • Translation • Rotation • Reflection • Dilation

    2. Isometry • An isometryis a transformation in which the preimage and the resulting image are congruent. • (you start with a preimage and after a transformation you have the image) • Translations, reflections and rotations are isometries, Dilations are not!

    3. Renaming Transformations It is common practice to name transformed shapes using the same letters with a “prime” symbol: It is common practice to name shapes using capital letters:

    4. Atranslation"slides" an object a fixed distance in a given direction.  The original object and its translation have the same shape and size, and they face in the same direction. Translations are SLIDES.

    5. Let's examine some translations related to coordinate geometry. The example shows how each vertex moves the same distance in the same direction. A to A’ is a vector <6, 0>

    6. Write the Points • What are the coordinates for A, B, C? • What are the coordinates for A’, B’. C’? • How are they alike? • How are they different?

    7. In this example, the "slide"  moves the figure7 units to the left and 3 units down. (or 3 units down and 7 units to the left.)

    8. Write the points • What are the coordinates for A, B, C? • What are the coordinates for A’, B’, C’? • How did the transformation change the points?

    9. Matrices and transformations • If a figure is translated 4 units to the right and 5 units down, <4, -5> you can use a matrix to find the coordinates of the image after the translation.

    10. Areflectioncan be seen in water, in a mirror, in glass, or in a shiny surface.  An object and its reflection have the same shape and size, but the figures face in opposite directions.  In a mirror, for example, right and left are switched.

    11. Line reflections are FLIPS!!!

    12. The line (where a mirror may be placed) is called the line of reflection.  The distance from a point to the line of reflection is the same as the distance from the point's image to the line of reflection. A reflection can be thought of as a "flipping" of an object over the line of reflection. If you folded the two shapes together line of reflection the two shapes would overlap exactly!

    13. What happens to points in a Reflection? • Name the points of the original triangle. • Name the points of the reflected triangle. • What is the line of reflection? • How did the points change from the original to the reflection?

    14. Reflections over the x and y axis • To reflect over the y axis give each x coordinate the opposite sign and keep the y coordinate the same. • To reflect over the x axis give each y coordinate the opposite sign and keep the x coordinate the same.

    15. A rotationis a transformation that turns a figure about a fixed point called the center of rotation.  An object and its rotation are the same shape and size, but the figures may be turned in different directions.

    16. Rotations are TURNS!!! The concept of rotations can be seen in wallpaper designs, fabrics, and art work.

    17. Clockwise Counterclockwise This rotation is 90 degrees counterclockwise.

    18. Rotations in the coordinate plane • 180 degrees- change both signs • 90 degrees CW or 270 degrees CCW make the x coordinate the opposite sign and switch x and y • 90 degrees CCW or 270 degrees CW make the y coordinate opposite and switch the x and y.

    19. Adilationis a transformation that produces an image that is the same shapeas the original, but is a different size. A dilation used to create an image larger than the original is called an enlargement.  A dilation used to create an image smaller than the original is called a reduction.

    20. Dilations always involve a change in size. Notice how EVERY coordinate of the original triangle has been multiplied by the scale factor (x2).

    21. How do we locate dilation images? • A dilation is a transformation who preimage and image are similar. A dilation is not an isometry. • Every dilation has a center and a scale factor n, n >0. The scale factor describes the size change from the original figure to the image.

    22. Example 1: • Quadrilateral ABCD has vertices A(-2, -1), B(-2, 1), C(2, 1) and D(1, -1). • Find the coordinates of the image for the dilation with a scale factor of 2 and center of dilation at the origin. C’ B’ B C A D A’ D’

    23. F(-3, -3), O(3, 3), R(0, -3) Scale factor 1/3 Example 2: O O’ F’ R’ F R

    24. Finding a Scale Factor • The blue quadrilateral is a dilation image of the red quadrilateral. Describe the dilation.

    25. REVIEW: Answer each question……………………….. Does this picture show a translation, rotation, dilation, or reflection? How do you know? Rotation

    26. Does this picture show a translation, rotation, dilation, or reflection? How do you know? Dilation

    27. Does this picture show a translation, rotation, dilation, or reflection? How do you know? (Line) Reflection

    28. Which of the following lettered figures are translations of theshape of the purple arrow?  Name ALL that apply. Explain your thinking. Letters a, c, and e are translations of the purple arrow.

    29. Has each picture been rotated in a clockwise or counter-clockwise direction? The birds were rotated clockwise and the fish counterclockwise.

    30. Basically, a tessellation is a way to tile a floor (that goes on forever) with shapes so that there is no overlapping and no gaps.

    31. Dutch graphic artist M. C. Escher (1898-1972) is known for his creative use of tessellations in his work. What transformations can you see in this picture? The birds and fish have been translated here.

    32. What transformations can you see in this Escher print? Some birds have been translated and some have been rotated.

    33. Can you name examples in real life of each transformation? • Translation • Rotation • Reflection • Dilation

    34. Check out these sites: http://www.farraguttn.com/fhs/math/nctm/index.htm http://www.mathsnet.net/transformations/index.html http://www.mcescher.com/