Composing Reflections

The blue triange is being reflected over line m, then that image is being reflected over line n. Move the two lines around and watch the movements of the red triangle.

Sorry, the GeoGebra Applet could not be started. Please make sure that Java 1.4.2 (or later) is installed and active in your browser (Click here to install Java now)

Questions to think about:
1. What is happening to the red triangle? How are the red triangle's movements related to the original blue triangle?
2. Right-click on each of the vertices of the red triangle, then click "Trace On." Move the two lines around. What is happening? Did you expect that? Why is it happening?
3. What happens when lines m and n are on top of one another? Does that make sense?

Brian Bisignani, July 22, 2008, Created with GeoGebra