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Intermediate

No laughing matter

Two squares share a vertex. Each square contains a coloured rectangle with extended side. What’s green : blue? By Matthew Arcus.

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Video: Sticky corners

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Intermediate

Unring a bell

A square and an equilateral triangle. What’s the angle α?

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Intermediate

Playing fields

Show equality of the green and orange square playing field areas.

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Video: The punctured hexagon

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Intermediate

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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The hippodrome shadow

The racer at A is running counter-clockwise around the inside of the outer purple circle, with a “shadow racer” B following behind, related by the three chords that are tangent to the inner orange circle. Does the shadow B ever catch up with A?

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Intermediate

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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