A square and a rectangle share a vertex. Two triangle areas are given. What is the total area?
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The voting pencil
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Out of focus
A semicircle with an inscribed triangle. Both circles are tangent to the semicircle, the diameter and one other triangle side. Prove that the line segment connecting the two shown tangency points is parallel to the diameter.
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The pentagon attack
Two regular pentagons and two diagonals. What’s the angle α?
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The red triangle
A square containing an isosceles triangle with given side lengths. What fraction is red?
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As within, so without
A semicircle and a circle are tangent. The tangency point is shown. Prove that the two coloured triangles are similar.
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Confined enclosure
A square containing four smaller squares. What fraction of its area is orange?
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Lean on me
Two squares and two diagonals. Prove that the angles α and β are equal.
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The sacrosanct circles
Two tangent circles and two tangent line segments meeting in a point on the outer circle. The tangency points are connected by a line segment of length x. What’s x in terms of a and b?
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The sliding ladder
A ladder seen from the side is sliding down a wall. Prove that a fixed point on the ladder traces part of an ellipse.
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Check and balance
A square divided by three line segments. The red and blue areas are equal. What’s the length proportion a : b?