The SSS criterion (by rigid motions)
- Three of the six — 3 tasks
- The two places the corner can go — 3 tasks
- Bringing one pair of sides together — 3 tasks
- One reflection finishes it — 3 tasks
- Going Deeper — 7 tasks
- Practice — 23 tasks
- Summary — 2 tasks
- Cool-down — 3 tasks
Classroom activities
Things a class does rather than writes on. Each one is a finished PDF: print it, cut it up if it says so, and hand it round.
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Does SSS Prove It? — Cut & Glue Sort 25 minutes, including the cutting · 5 sheets
12 pairs of triangles with tick marks, side lengths or a shared side, sorted into congruent by SSS, not congruent, and cannot tell. A kite with two ticked pairs and a shared side waits in the first row; two ticked pairs drawn exactly alike wait in the last.
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SSS: Lengths First, Letters Second — Answer Maze 10–15 minutes · 4 sheets
8 boxes on one page, each two lettered triangles with their side lengths or tick marks, turned or flipped: which congruence statement is right? A wrong answer pairs the corners by where they sit on the page, or writes the letters in the order they come, and goes to a box that sends the student back; the row of box numbers at the foot is the check.
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Does SSS Prove It? — Mystery Picture 25–35 minutes · 4 sheets
25 squares, each a pair of triangles drawn with tick marks or described in words: fill the square if SSS proves them congruent. Shared sides count as a pair and mirror images are congruent; two ticked pairs, equal angles and near misses are not enough. When every square is right, the letter L appears.