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Cut Equilateral Triangles into Rectangles & Dudeney's Puzzle

A quadrilateral can be dissected into a rectangle by a line joining the mid-points of one pair of opposite sides, and the perpendiculars to this line from the mid-points of the other pair of opposite sides (see ). In this applet, the equilateral triangle is dissected into 4 pieces by the 3 lines. Rotate the dissections, drag the red points to get a rectangle. CLICK any black SEGMENT to show/hide its LENGTH. Drag Q to investigate its position at which the rectangle becomes a square (the Dudeney's Puzzle).
Anthony Or. GeoGebra Institute of Hong Kong.