Two figures with the same shapes but different sizes. This should be written on the board. A student asked if circles are similar. Yes!

 

I said to a girl, “Remember when you were a little girl? Same shape, different size. This is similarity!”

 

The classroom discussion was similar triangles. One student did a problem on the board, and used the word “stereo” instead of “similar”. It is interesting to try to understand the error. Maybe since the student saw two triangles on the board, he was thinking of a pair of stereo receivers.

 

Subject matter was similar triangles. One student proved a problem, using, according to the student, the “AAA postulate.” This is somewhat confusing, as there is no AAA postulate. Instead, AAA is the definition of similar triangles, and AA is a theorem (not a postulate).