Regular polygons and circles

  • Bicentric Quadrilaterals
    problem

    Bicentric quadrilaterals

    Age
    14 to 16
    Challenge level
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    Investigate the properties of quadrilaterals which can be drawn with a circle just touching each side and another circle just touching each vertex.
  • LOGOSquares
    problem

    LOGOsquares

    Age
    16 to 18
    Challenge level
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    Ten squares form regular rings either with adjacent or opposite vertices touching. Calculate the inner and outer radii of the rings that surround the squares.

  • Circles ad infinitum
    problem

    Circles ad infinitum

    Age
    16 to 18
    Challenge level
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    A circle is inscribed in an equilateral triangle. Smaller circles touch it and the sides of the triangle, the process continuing indefinitely. What is the sum of the areas of all the circles?

  • Ball bearings in a metal wheel.
    problem

    Ball bearings

    Age
    16 to 18
    Challenge level
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    If a is the radius of the axle, b the radius of each ball-bearing, and c the radius of the hub, why does the number of ball bearings n determine the ratio c/a? Find a formula for c/a in terms of n.

  • So Big
    problem

    So big

    Age
    16 to 18
    Challenge level
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    One side of a triangle is divided into segments of length a and b by the inscribed circle, with radius r. Prove that the area is: abr(a+b)/ab-r^2
  • Orthogonal Circle
    problem

    Orthogonal circle

    Age
    16 to 18
    Challenge level
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    Given any three non intersecting circles in the plane find another circle or straight line which cuts all three circles orthogonally.

  • Ford Circles
    problem

    Ford circles

    Age
    16 to 18
    Challenge level
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    Can you find the link between these beautiful circle patterns and Farey Sequences?

  • A rational search
    problem

    A rational search

    Age
    16 to 18
    Challenge level
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    Investigate constructible images which contain rational areas.