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10-9 Reflections (page 456-459)

10-9 Reflections (page 456-459). Indicators  G7-Identify the line & rotation symmetries of 2-d figures to solve problems. G8-Perform reflections of 2-d figures using a variety of methods. Reflections…. Figures that match exactly when folded in half have line symmetry .

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10-9 Reflections (page 456-459)

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  1. 10-9 Reflections (page 456-459) Indicators G7-Identify the line & rotation symmetries of 2-d figures to solve problems. G8-Perform reflections of 2-d figures using a variety of methods.

  2. Reflections… Figures that match exactly when folded in half have line symmetry. Each fold line is called a line of symmetry. Some figures can be folded in more than one way to show symmetry.

  3. You try… • Determine whether each figure has line symmetry. If so how many? Where?

  4. Reflection(flip) • A type of transformation where a figure is flipped over the line of symmetry is a reflection. • Think of a mirror image. • As with translations, the original figure and reflected image are congruent. • Helpful Hints! • When reflecting over the x-axis, change the y-coordinate to their opposites. • When reflecting over the y-axis, change the x-coordinate to their opposites.

  5. Example: Reflect a figure over the x-axis. Quadrilateral QRSThas vertices Q (-1,1), R (0,3), S (3,2), T (4,0). Find the coordinates of QRST after a reflection over the x-axis. Then graph the figure and its reflected image. R S Q T T’ Q’ S’ R’ The coordinates for the reflected image are Q (-1,-1), R (0,-3), S (3, -2), T (4,0). Check out the y-coordinates!

  6. Example 2: Reflect a figure over the y-axis. Triangle XYZhas vertices X (1,2), Y (2,1), Z (1,-2). Find the coordinates of XYZ after a reflection over the y-axis. Then graph the figure and its reflected image. X X1 Y Y1 Z1 Z The coordinates for the reflected image are X (-1,2), Y (-2,1), Z (-1,-2). Check out the x-coordinates!

  7. Example 3: Reflect a figure over the x-axis. Triangle XYZhas vertices X (1,2), Y (2,1), Z (1,-2). Find the coordinates of XYZ after a reflection over the x-axis. Then graph the figure and its reflected image. Z’ X Y Y’ Z X’ The coordinates for the reflected image are X (1,-2), Y (2,-1), Z (1,2). Check out the y-coordinates!

  8. Homework • 10-8 pg. 453-454 #6-12 e, 16-26 a • 10-9 pg. 459 #16-27 a

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