A Mathematical Tribute to the Soccer Ball

(nytimes.com)

15 points | by igonvalue 3 days ago

2 comments

  • pmdulaney 3 days ago
    If every black pentagon shares a face with 5 hexagons, and every white hexagon shares a face with 3 pentagons, can you determine the ratio of hexagons to pentagons?

    (I haven't solved this problem, but I think it is doable.)

    • gus_massa 1 day ago
      Tip: Count the edges. Imagine each edge has two sides/ribons. One side/ribon is white and the other is black.
      • C-x_C-f 7 hours ago
        You can even find the exact number of pentagons (or hexagons, or edges, or vertices) using the equation

        V - E + F = 2

        where V, E, F are the number of vertices, edges, and faces, respectively.

        This holds for any polyhedron (and other shapes have similar equations possibly with a different right hand side) and the left hand side is called the Euler characteristic of the soccer ball (or any polyhedron).

        Spoiler warning: the Wikipedia article for the Euler characteristic [0] has a worked out example specifically for the soccer ball.

        [0] https://en.wikipedia.org/wiki/Euler_characteristic

  • vismit2000 7 hours ago