Extra Information: Triangle Congruence

I meant to blog about this activity last year and now I've already used it a second time. The activity, pictures, and explanation can all be found here.

My summary: students are given four pieces of information and a congruence postulate/theorem. They mark all four pieces on the triangles then decide which piece was the 'extra' information.

My modifications:

1. I printed the two triangles on pretty card stock for each student and slid it in a page protector so students could mark with dry erase markers then record answers on their paper answer sheet.

2. I made the answer key into a Powerpoint to show students after the activity is complete.

Both years I used this after introducing the triangle postulates and theorems. I started the class by handing each student a triangle with markings (from a Kagan book) and signs hung around the room. They look at their triangle and then go stand in the correct corner. They compare with others in their corner. I check, correct, and then repeat.

Then comes the extra information activity.

Reasons I love it:

  • It's not a handout/worksheet/packet
  • There is movement: students get up to trade bags or retrieve bags from designated home after working each problem
  • They get to use dry erase markers: which translates to 1000 times more productivity
  • It clears up many misconceptions: when to mark tick marks, when to mark rainbows, where to mark tick marks, where to mark rainbows, what order to read the markings in, what each postulate/theorem must have to be correct, how each postulate/theorem can look in different combinations, and how parts of two triangles can match or be matched
  • It helps students get comfortable with determining the correct postulate/theorem
  • It works
  • It's colorful
  • It doesn't involve me talking...or really doing anything
  • It's not a handout/worksheet/packet

If you never clicked the link at the top...you really should. I download all recommended activities even if I don't know when or if I'll use them. You never know what you might need!


  1. First, I feel like a minor celebrity! I've been reading your blog forever :) I just found out that I'm teaching geometry next year at a new school and wanted to see if I could come up with anything new and interesting. I'm glad you like this!

    Second, I'm an activity hoarder too. I have folders and folders of materials for classes I've never even taught.

    1. *feel like I've MET a minor celebrity

    2. It's a great activity!!! I immediately download any activity I find just in case the author takes it down or the Internet goes away forever. lol I like to b prepared!