Categories

## Three times three

A regular nonagon and two equilateral triangles. What’s the angle α?

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## The laser game

In an equilateral triangular mirror room a laser is shot from the top vertex down to the base. The light ray bounces three times to return to the same base point. What is the angle α?

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## The hex division

A regular hexagon with two diagonals and two perpendiculars. What’s red : yellow?

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## The owl of Ceva

A triangle with three concurring cevians. What’s orange : blue?

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## In the red

Two congruent semicircles with their centres and a chord. Prove that the two red triangles are congruent as well.

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## The vanilla ice cream

A regular pentagon with two extended sides and a right angle. What is blue : green?

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## Wheel of fortune

A unit square and a point on the inscribed circle. What is a2+b2+c2+d2?

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## Peekaboo

Three congruent squares share two vertices while the upper sides coincide. What’s red : blue?

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## Falling pillar II

Three congruent rectangles on a line. Prove that the four red points are cyclic.

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## The falling pillar

Three congruent rectangles on a line. What’s the angle α?