A regular nonagon and four equilateral triangles. The purple and yellow triangles share a vertex. Prove that the yellow triangles also share a vertex.
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In touch
Tag: triangle
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The party hat II
An equilateral triangle with a circular arc through its red centre and two vertices. If the yellow area equals the green one, what’s the angle α?
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The lighthouse
A parallelogram and four equilateral triangles. What is yellow : green?
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Holes in my heart
The heart is divided into right triangles, each of which contains a blue circle. What is the total circumference of the blue circles in relation to the green perimeter and the lengths of the purple and orange lines in the centre?
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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?