Choosing a criterion from a marked figure
- Between, and not between — 3 tasks
- The name read off the page — 3 tasks
- Where the marked angle sits — 3 tasks
- The pair the figure gives for free — 3 tasks
- What one more given buys — 6 tasks
- Practice — 24 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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Marks Alone, a Free Pair, or Not Proved? Choosing a Criterion — Cut & Glue Sort 25 minutes, including the cutting · 5 sheets
12 pairs of marked triangles sorted into three rows: proved by the marks alone, proved only with a pair the figure gives for free (a shared side or vertical angles), and not proved. The last row holds pairs that share a side or cross and still prove nothing, and pairs drawn alike whose marks prove nothing.
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Which Criterion, or None? Choosing a Congruence Criterion — Answer Maze 10–15 minutes · 4 sheets
8 boxes on one page, each a pair of marked triangles or three written rows: which criterion proves them congruent, or is nothing proved? The wrong answers are the two mistakes this lesson exists to stop: missing the pair a figure gives with no mark (a shared side, vertical angles), and misreading where a part sits (SSA for SAS, ASA for AAS). The row of box numbers at the foot is the check.
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Proved or Not Proved? Choosing a Congruence Criterion — Mystery Picture 25–35 minutes · 4 sheets
25 squares, each a pair of marked triangles or three written facts: do they prove the triangles congruent? Fill the square if SSS, SAS, ASA, AAS or HL fits, leave it white if nothing does. Some pairs need a side the two triangles share or the vertical angles at a crossing; some look congruent and are not proved. When every square is right, a letter appears.