The AA criterion (by rigid motions)
- One mark, and what it settles — 3 tasks
- The third angle comes free — 3 tasks
- Dilate first, then finish — 3 tasks
- Where the second pair hides — 3 tasks
- Equal angles outside triangles — 5 tasks
- Practice — 25 tasks
- Summary — 2 tasks
- Cool-down — 6 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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Where Is the Second Pair of Angles? The AA Rule — Cut & Glue Sort 25 minutes, including the cutting · 5 sheets
12 pairs of triangles marked with arcs and right-angle squares, sorted by where the second pair of equal angles comes from: both pairs marked, one marked and one hidden in the drawing (a shared corner, two segments crossing, two right angles), or only one pair, so you cannot tell. No numbers anywhere.
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Two Angles, or Not Enough? The AA Rule — Answer Maze 10–15 minutes · 4 sheets
8 boxes on one page: are the two triangles similar, which angle matches which, and what does similar promise about the sides? The wrong answers are the two mistakes this lesson exists to stop: counting the pairs of equal angles wrongly (wanting all three, taking one as enough, missing a shared angle or a crossing), and matching angles by the order of the letters. The row of box numbers at the foot is the check.
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Do Two Angles Make Them Similar? The AA Rule — Mystery Picture 25–35 minutes · 4 sheets
25 squares, each two marked triangles or a sentence about two triangles: do you know two pairs of equal angles? Fill the square if the triangles must be similar, leave it white if you cannot tell. The second pair often hides: a corner both triangles share, two segments that cross, parallel sides, two right angles. No numbers anywhere. When every square is right, a number appears.