Four squares and one centre. Prove that the red quadrilateral is a parallelogram.
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Dancing squares
Tag: parallelogram
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Triangles galore
Four equilateral triangles. Two centres are shown. Prove that the green quadrilateral is a parallelogram.
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The lighthouse
A parallelogram and four equilateral triangles. What is yellow : green?
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Pink parallels
A pink parallelogram with two extended sides. What’s α : β?
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Three’s a crowd
Four equilateral triangles. Prove that the red quadrilateral is a parallelogram.
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The gyroscope
Two ellipses go through each others focal points. Prove that the focal points are the vertices of a parallelogram.
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The beam in your eye
Three parallelograms are inscribed in a circle. Prove that the common red vertex is the orthocentre of the dashed triangle.
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The iron curtain
A parallelogram ABCD with a circle and a diameter CE. Prove that point E is the orthocentre of triangle ABD.
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The crazy quilt
A parallelogram is divided into several areas. What is the area X of the blue trapezium?
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Out of proportion
An equilateral triangle containing a parallelogram, another equilateral triangle and a circular arc that is tangent in its base vertices. What is the proportion pink : blue?