A little background

Objectives

  • Students learn the definition of dilation and why “same shape” is not good enough to say two figures are similar.
  • Students know that dilations magnify and shrink figures.
  • Students learn how to use a compass and a ruler to perform dilations.
  • Students learn that dilations map lines to lines, segments to segments, and rays to rays. Students know that dilations are degree preserving.
  • Students know that dilations map circles to circles and ellipses to ellipses with the same shape.
  • Students know that to shrink or magnify a dilated figure back to its original size from center 0 with scale factor r you must dilate the figure by a scale factor of 1/r.
  • Students experimentally verify the properties related to the Fundamental Theorem of Similarity (FTS).
  • Students verify the converse of the Fundamental Theorem of Similarity experimentally.
  • Students apply the Fundamental Theorem of Similarity to find the location of dilated points on the plane.
  • Students describe the effect of dilations on two - dimensional figures using coordinates.
  • Students know an informal proof of why dilations are degree - preserving transformations.
  • Students know an informal proof of why dilations map segments to segments, lines to lines , and rays to rays.

Prior Knowledge

  • GeometryRigid Motions
  • Geometry2-D Shapes
8.G.A.3
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