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Author: Rik D. Tangerman
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Family constellation
Two equilateral triangles on a line. Prove that the blue triangle is equilateral as well.
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Video: Quad stretches
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Tipping point II
Two regular pentagons share a vertex. What’s the angle α?
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All connected
Four coloured rectangles and three line segments. Prove that the three line segments are concurrent.
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Video: A devious cevian
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Video: Ends of the spectrum
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Ten to nine
Two triangles and one incircle with its centre and tangency points. Prove that the triangles are similar.
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Video: Square mouse
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Quad stretches
Two squares sharing a vertex and two overlapping coloured quadrilaterals from square side midpoints. What is the area proportion of the blue and the red quadrilateral?