Exploring with Reflection over a Line
The following applet allows you to explore with a triangle reflection over a line. Your goal is to take the blue triangle and drag A'', B'', and C'' so that it matches the reflection of the pre-image of triangle with vertices A, B, and C. When you think you have the correct reflection of the image, check "Check Answer" and you will be able to see if you have correctly moved the vertices. To refresh the picture and try again, refresh your window or hit CTRL-R.
Jot down the coordinates of A, B, and C. When you are able to correctly match up the reflection of this image, jot down the correct coordinates for A'', B'', and C''. What do you notice? Continue to jot down the coordinates of the pre-image and image and see if you can make a conjecture about rotation about a line.