b. Angles are taken to angles of the same measure.

Jenny is in kindergarten and loves finger painting. Last week, she spent hours on her masterpiece: a picture of an angle. It looked kind of like this (except that it was purple and orange and green and pink):

Jenny was incredibly proud of her impressive angle and couldn't wait to bring it home to show her parents. She very carefully folded her paper so the artwork wouldn't get ruined. But when she proudly opened her backpack and took out the picture, Jenny was surprised to see that it looked like this:

It was still purple and orange and green and pink, but there were two identical angles instead of just one. Jenny giggled with delight and said, "Ah, this is an example of a mathematical transformation! It's a line reflection." By the way, did we mention Jenny was a child genius?

Even when Jenny's angle was reflected across a line, it resulted in an angle that was identical to the original angle in measure. In other words, the wideness or narrowness of the angle stayed the same. After a bit of exploration with angles, students should come to the conclusion that this is true for translation and rotation also—the angles' measures will stay the same.