Four equilateral triangles. Prove that the red quadrilateral is a parallelogram.
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Three’s a crowd
Tag: triangle
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North by Northwest
An equilateral triangle and a rectangle. What’s the angle α?
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Along similar lines
The blue triangle is similar to the green one and has the same orientation. The midpoints between corresponding vertices are connected to form a red triangle. Prove that it is also similar.
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Rule of 72
Two triangles and an extended side. What’s blue : orange?
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Outside the frame
Two squares and an equilateral triangle. Prove that the area of the triangle plus the small square equals that of the large square.
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The odd balance
Two circles are tangent to two perpendicular lines and have their centres connected. Prove that the green triangle is right isosceles.
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The weather balloon
A circle with three red tangents. The tangency points are marked red. Prove that the yellow triangle is isosceles.
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A square deal II
A regular hexagon and a square share a vertex. What’s green : red?
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And rightly so
A regular hexagon with a diagonal and a right triangle. What fraction is orange?
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Count to five
A triangle with a cevian. What’s α?