CPCTC
- Three marked, three not — 3 tasks
- Into the congruence, and out of it — 3 tasks
- Where a CPCTC row comes from — 6 tasks
- The two-stage proof — 3 tasks
- Arguments that establish nothing — 6 tasks
- Practice — 21 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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What Does CPCTC Give? — Cut & Glue Sort 25 minutes, including the cutting · 5 sheets
12 pieces, each three given facts about two triangles and one more pair of matching parts. Sort them: already given, new from CPCTC, or CPCTC cannot be used because the facts do not prove the triangles congruent (SSA, or three angles).
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CPCTC: Into or Out of a Congruence? — Answer Maze 10–15 minutes · 4 sheets
8 written boxes on one page about two triangles: which reason fits the row, what CPCTC gives, and whether a proof is finished or uses what it has to prove. The wrong answers are the mistakes this lesson exists to stop. The row of box numbers at the foot is the check.
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Is the Reason Right? CPCTC or a Criterion — Mystery Picture 25–35 minutes · 4 sheets
25 squares, each three given facts about two triangles and one row of a proof with its reason: fill the square if the reason is right. A criterion proves the triangles congruent; CPCTC comes after, for one pair of parts, and only when the facts prove the congruence. When every square is right, a letter appears.