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Author: Rik D. Tangerman
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The doubleganger
Two nested right triangles with their incircles. Two tangency points are shown. Prove that the red and yellow line segments are parallel.
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Video: Wedge the wedge
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Cherries
Two tangent circles and two green tangents. The three tangency points are shown in black. Prove that the blue line segment is a common tangent.
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Video: Blowing bubbles
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Sticky corners
Two equilateral triangles and several line segments. What is red : yellow?
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Video: Vanishing point II
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The punctured hexagon
A regular hexagon, a square and an equilateral triangle. Show that the top vertex of the triangle is on the hexagon circumcircle.
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Video: Balancing Act II
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Wedge the wedge
An equilateral triangle containing an isosceles triangle that is not equilateral. What’s the angle α?