# The Magic Octagon – Understand Congruence in Terms of Rigid Motions

Before we go into this amazing lesson that will have your students so engaged you won't be able to get them to stop talking about it the rest of the day, let me show you the standard in which the lesson is based on. Understand congruence in terms of rigid motions.

#### Understand Congruence in Terms of Rigid Motions

CCSS.MATH.CONTENT.HSG.CO.B.6
Use geometric descriptions of rigid motions to transform figures and to predict the effect of a given rigid motion on a given figure; given two figures, use the definition of congruence in terms of rigid motions to decide if they are congruent.

## Now that the Boring Part is over... On to the lesson!

Dan Meyers' Magic Octagon!

Have the students predict which way the arrow will go. Ask them to pick what time the hand will be on after rotated. Here's a hint: 99% of them (probably 100% but some will just guess the opposite of everyone else because that is what they always do with no rhyme or reason to their guess) will get it wrong, including you!  🙂

Don't play the video for them! Actually make the Octagon and do the activity with the class. Then lead the discussion on Rigid Motion. The hard part won't be getting them to talk about this. The hard part will be to get them to stop talking about this!

Tip: The class will get a little loud when you reveal the results, be ready!

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