Dilations (Day 2)

50 Minute Class, Curriculum, Geometry

Learning Goal: Develop understanding of why dilations work as well as procedural fluency.




  • Common Core
    • HSG.CO.A.2 – Represent transformations in the plane using, e.g., transparencies and geometry software; describe transformations as functions that take points in the plane as inputs and give other points as outputs. Compare transformations that preserve distance and angle to those that do not (e.g., translation versus horizontal stretch).
  • TEKS
    • G.3(B) – determine the image or pre-image of a given two-dimensional figure under a composition of rigid transformations, a composition of non-rigid transformations, and a composition of both, including dilations where the center can be any point in the plane
    • G.3(C) – identify the sequence of transformations that will carry a given pre-image onto an image on and off the coordinate plane

2 thoughts on “Dilations (Day 2)

  1. Dane,

    On the ungraded formative assessment/spiraling practice, I’m stuck on a question. It’s the first question on the spiraling practice that involves finding angle E. Are you supposed to find a numerical answer or just an expression/idea?

    Thanks for all you do,
    Kevin Grogaard

    1. Hey Kevin,

      Thanks for the comment. After trying it again myself, I couldn’t come up with logic to get an answer (I was looking for a numerical answer, 120 degrees). So, I went ahead and added more given information (AC bisects angle FCB). Here’s my solution after the new information is given.

      I think I found the problem somewhere and tried to get too cute when making it more challenging. Thanks for asking about it! Let me know if that works.

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