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  2. Heesch's problem - Wikipedia

    en.wikipedia.org/wiki/Heesch's_problem

    Heesch's problem is the problem of determining the set of numbers that can be Heesch numbers. Both are named for geometer Heinrich Heesch , [ 1 ] who found a tile with Heesch number 1 (the union of a square, equilateral triangle, and 30-60-90 right triangle) [ 2 ] and proposed the more general problem.

  3. Special right triangle - Wikipedia

    en.wikipedia.org/wiki/Special_right_triangle

    Then ABD is a 30°–60°–90° triangle with hypotenuse of length 2, and base BD of length 1. The fact that the remaining leg AD has length √ 3 follows immediately from the Pythagorean theorem. The 30°–60°–90° triangle is the only right triangle whose angles are in an arithmetic progression.

  4. Ellsberg paradox - Wikipedia

    en.wikipedia.org/wiki/Ellsberg_paradox

    When faced with the choice between a red ball and a black ball, the probability of ⁠ 30 / 90 ⁠ is compared to the lower part of the ⁠ 0 / 90 ⁠ – ⁠ 60 / 90 ⁠ range (the probability of getting a black ball). The average person expects there to be fewer black balls than yellow balls because, in most real-world situations, it would be ...

  5. Rep-tile - Wikipedia

    en.wikipedia.org/wiki/Rep-tile

    A right triangle is a triangle containing one right angle of 90°. Two particular forms of right triangle have attracted the attention of rep-tile researchers, the 45°-90°-45° triangle and the 30°-60°-90° triangle.

  6. List of NP-complete problems - Wikipedia

    en.wikipedia.org/wiki/List_of_NP-complete_problems

    The problem for graphs is NP-complete if the edge lengths are assumed integers. The problem for points on the plane is NP-complete with the discretized Euclidean metric and rectilinear metric. The problem is known to be NP-hard with the (non-discretized) Euclidean metric. [3]: ND22, ND23

  7. Polydrafter - Wikipedia

    en.wikipedia.org/wiki/Polydrafter

    306090 triangle. In recreational mathematics, a polydrafter is a polyform with a 30°–60°–90° right triangle as the base form. This triangle is also called a drafting triangle, hence the name. [1] This triangle is also half of an equilateral triangle, and a polydrafter's cells must consist of halves of triangles in the triangular ...

  8. Ailles rectangle - Wikipedia

    en.wikipedia.org/wiki/Ailles_rectangle

    A 30°–60°–90° triangle has sides of length 1, 2, and . When two such triangles are placed in the positions shown in the illustration, the smallest rectangle that can enclose them has width 1 + 3 {\displaystyle 1+{\sqrt {3}}} and height 3 {\displaystyle {\sqrt {3}}} .

  9. Algebra and Tiling - Wikipedia

    en.wikipedia.org/wiki/Algebra_and_Tiling

    Chapter five considers Monsky's theorem on the impossibility of partitioning a square into an odd number of equal-area triangles, and its proof using the 2-adic valuation, and chapter six applies Galois theory to more general problems of tiling polygons by congruent triangles, such as the impossibility of tiling a square with 30-60-90 right ...