Explaining, convincing and proving
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problemTriangular Intersection
What is the largest number of intersection points that a triangle and a quadrilateral can have?
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problemPolycircles
Show that for any triangle it is always possible to construct 3 touching circles with centres at the vertices. Is it possible to construct touching circles centred at the vertices of any polygon?
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problemTriangle Incircle Iteration
Keep constructing triangles in the incircle of the previous triangle. What happens?
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problemDiophantine N-Tuples
Can you explain why a sequence of operations always gives you perfect squares?
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problemDOTS Division
Take any pair of two digit numbers x=ab and y=cd where, without loss of generality, ab > cd . Form two 4 digit numbers r=abcd and s=cdab and calculate: {r^2 - s^2} /{x^2 - y^2}.
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problemNo Right Angle Here
Prove that the internal angle bisectors of a triangle will never be perpendicular to each other.
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problemFixing the Odds
You have two bags, four red balls and four white balls. You must put all the balls in the bags although you are allowed to have one bag empty. How should you distribute the balls between the two bags so as to make the probability of choosing a red ball as small as possible and what will the probability be in that case?
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problemThe Pillar of Chios
Semicircles are drawn on the sides of a rectangle. Prove that the sum of the areas of the four crescents is equal to the area of the rectangle.
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problemEncircling
An equilateral triangle is sitting on top of a square. What is the radius of the circle that circumscribes this shape?