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im.g.1.11.3.Triangle in the Mirror

Kiran started reflecting triangle CDE across line m. So far, he knows the image of D is D', and the image of E is E'.
1. Mark up the drawing to show how he reflected point D. 2A. Use the straightedge and compass moves to determine the location of C'. 2B. Use the reflection tool provided to verify you are correct. 2C. Once you've correctly determined the location of C', use the polygon tool to shade in triangle C'D'E'.

3. Write a set of instructions for how to reflect any point, P, across a given line, m.

4. Elena found C' incorrectly. (See below). Elena is convinced that triangle C'D'E' "looks fine." Explain to Elena why her C' is not a reflection of point C across line m.


illustrative mathematics. geometry. unit 1. lesson 11. activity 3 Triangle in the mirror. Licensed under the Creative Commons Attribution 4.0 license