Trapezoids: the midsegment theorem and isosceles trapezoids
- Halfway up a leaning board — 3 tasks
- Bases, legs, and the leg rule — 3 tasks
- The midsegment averages the bases — 6 tasks
- Equal base angles, equal legs — 3 tasks
- Going Deeper — 6 tasks
- Practice — 25 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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True for Every Trapezoid, or Only Some? — Cut & Glue Sort 25 minutes, including the cutting · 5 sheets
12 sentences about trapezoids, sorted into "true for every trapezoid", "true for every isosceles trapezoid but not every trapezoid" and "not true for every isosceles trapezoid". It pulls the facts about all trapezoids (the angles on a leg, the midsegment) apart from the isosceles package, and the last row holds the lesson's surprise: the diagonals of an isosceles trapezoid are congruent but do not bisect each other.
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Halfway, or Just Subtracted? Trapezoid Midsegments and Base Angles — Answer Maze 10–15 minutes · 4 sheets
8 boxes on one page. Half find a midsegment or a missing base; half find an angle of a trapezoid from one given angle. The wrong answers are the lesson's two big mistakes: subtracting (or adding without halving) instead of taking the average, and mixing up the two angles that share a base with the two angles on a leg. The row of box numbers at the foot is the check.
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Is It Really an Isosceles Trapezoid? — Mystery Picture 25–35 minutes · 4 sheets
25 squares, each a quadrilateral with arrowheads, arcs, right-angle marks, ticks or printed numbers: fill the square only if the marks prove it is an isosceles trapezoid (parallel bases and a pair of congruent base angles). The figures are turned every way, so the equal pair is not always at the bottom. Congruent legs alone, angles on one leg, and figures that only look isosceles stay white. When every square is right, a picture appears.
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Where Is Halfway Between the Bases? Trapezoid Midsegments — Scavenger Hunt a full class period · 13 sheets
16 cards around the room, each one tilted, scalene trapezoid with its midsegment. Some cards give the two bases and ask for the midsegment; the others give the midsegment and one base and ask for the other base. Adding the bases without halving, or subtracting one length from the other, lands on a card that sends the group back, and a clean run is 8 lines on the record sheet.