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Advanced

Drop shadow II

A right isosceles triangle contains another triangle. What is the angle α? Advanced if no trigonometry is used.

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Intermediate

The telescope

The odd regular polygons are stacked together, in increasing order, zigzagging to form a telescope that extends forever! What is the limiting angle (with respect to the horizontal) at which the telescope points?

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Intermediate

The weight lifter

Express the x coordinate of E in terms of x coordinates of A, B, F, and G. The two black lines are supposed to be parallel to the x-axis.

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Beginner

Outside the pentagon

A regular pentagon and two coloured equilateral triangles. What is the angle α?

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Intermediate

Baby block II

A square containing another square with an extended side. What is tan(α) in terms of the red and green segment lengths?

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Beginner

The boomerang

A quadrilateral and a triangle. What’s the angle α?

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Intermediate

The pentagon proportion

A regular pentagon and a circular arc through its red centre. What’s the proportion α : β?

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Advanced

Baby steps

The edges of a cyclic quadrilateral extend to two intersections. O is the circle centre. The two diagonals intersect inside the circle. What is the angle α?

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Intermediate

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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Beginner

Tip of the veil

A square with two right angles. What fraction is yellow?