Isosceles and equilateral triangles
- The line you did not pay for — 3 tasks
- Which angle is opposite which side — 3 tasks
- The base angles theorem and its converse — 12 tasks
- All three sides, all three angles — 6 tasks
- Going Deeper — 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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The Base Angles Theorem, the Converse, or Neither? — Cut & Glue Sort 25 minutes, including the cutting · 5 sheets
12 marked triangles, each with a written conclusion, sorted into three rows: the base angles theorem gives it, the converse gives it, or the marks do not give it. The last row holds the mistake that costs the most on tests: a conclusion about the wrong pair of parts.
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Which Angles Are Equal? Isosceles Triangles — Answer Maze 10–15 minutes · 4 sheets
8 boxes on one page, each one triangle with ticks or arcs: find the angle or side asked for, or decide that it cannot be found. The wrong answers are the two mistakes this lesson exists to stop — taking the two bottom angles as the equal pair, and trusting the look of the triangle instead of its marks. The row of box numbers at the foot is the check.
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Must These Two Angles Be Equal? Isosceles Triangles — Mystery Picture 25–35 minutes · 4 sheets
25 squares, each one triangle with ticks on its sides and two angles marked with a dashed arc: fill the square if the two angles must be equal, leave it white if not. The triangles rest on an equal side, stand upside down, or are tall and narrow, so the bottom two angles are not always the pair. When every square is right, a letter appears.
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Isosceles and Equilateral Triangles — Scavenger Hunt a full class period · 13 sheets
16 cards around the room, each one triangle with two equal sides marked by ticks, resting on one of those sides. One angle is given and one is asked. Taking the two angles at the bottom of the page as the equal pair lands on a card that sends the group back, and a clean run is 8 lines on the record sheet.