Two circles, one having its centre on the other, and four line segments. Prove that the three coloured line segments are congruent.

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geometry puzzles

Four orange unit circles and their red centres. What is the radius of the green circle? Kindly provided by Marshall W. Buck.

Two triangles and an extended side. What’s blue : orange?

- Tags angle, length, proportion, triangle

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- Post author By Rik
- Post date March 13, 2023
- No Comments on Sailing by night

A circle with an inscribed quadrilateral. Prove that ab=cd. Kindly provided by Marshall W. Buck.

- Tags circle, length, quadrilateral

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- Post author By Rik
- Post date March 10, 2023
- No Comments on The hawfinch II

A circle with two tangents. What’s red : blue in terms of α?

- Tags angle, circle, length, proportion

A triangle with a cevian. What’s α?

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- Post author By Rik
- Post date February 22, 2023
- 1 Comment on The truss bridge

Two lines connected by five triangles. Prove that orange = blue. Created by Marshall W. Buck.

- Tags length, proportion, triangle

A triangle with two angular bisectors. What’s the proportion blue : red?

- Tags angle, length, proportion, triangle

Two equilateral triangles and one centre. What’s green : red?

- Tags length, proportion, triangle

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- Post author By Rik
- Post date January 27, 2023
- 1 Comment on The Moroni minimum

An arbitrary point on the parabola y=x^{2}. Shown are the tangent in that point and a line segment perpendicular to it. What is the minimal height h?