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  2. Liu Hui's π algorithm - Wikipedia

    en.wikipedia.org/wiki/Liu_Hui's_π_algorithm

    The area within a circle is equal to the radius multiplied by half the circumference, or A = r x C /2 = r x r x π.. Liu Hui argued: "Multiply one side of a hexagon by the radius (of its circumcircle), then multiply this by three, to yield the area of a dodecagon; if we cut a hexagon into a dodecagon, multiply its side by its radius, then again multiply by six, we get the area of a 24-gon; the ...

  3. Dodecagon - Wikipedia

    en.wikipedia.org/wiki/Dodecagon

    Three squares of sides R can be cut and rearranged into a dodecagon of circumradius R, yielding a proof without words that its area is 3R 2. A regular dodecagon is a figure with sides of the same length and internal angles of the same size. It has twelve lines of reflective symmetry and rotational symmetry of order 12.

  4. Method of exhaustion - Wikipedia

    en.wikipedia.org/wiki/Method_of_exhaustion

    The area bounded by one spiral rotation and a line is 1/3 that of the circle having a radius equal to the line segment length; Use of the method of exhaustion also led to the successful evaluation of an infinite geometric series (for the first time);

  5. Rhombic dodecahedron - Wikipedia

    en.wikipedia.org/wiki/Rhombic_dodecahedron

    the radius of the sphere passing through the eight order three vertices is exactly equal to the length of the sides: = The surface area A and the volume V of the rhombic dodecahedron with edge length a are: [ 4 ] A = 8 2 a 2 ≈ 11.314 a 2 , V = 16 3 9 a 3 ≈ 3.079 a 3 . {\displaystyle {\begin{aligned}A&=8{\sqrt {2}}a^{2}&\approx 11.314a^{2 ...

  6. Measurement of a Circle - Wikipedia

    en.wikipedia.org/wiki/Measurement_of_a_Circle

    Proposition one states: The area of any circle is equal to a right-angled triangle in which one of the sides about the right angle is equal to the radius, and the other to the circumference of the circle. Any circle with a circumference c and a radius r is equal in area with a right triangle with the two legs being c and r.

  7. Regular dodecahedron - Wikipedia

    en.wikipedia.org/wiki/Regular_dodecahedron

    If the edge length of a regular dodecahedron is , the radius of a circumscribed sphere (one that touches the regular dodecahedron at all vertices), the radius of an inscribed sphere (tangent to each of the regular dodecahedron's faces), and the midradius (one that touches the middle of each edge) are: [21] =, =, =. Given a regular dodecahedron ...

  8. Icositetragon - Wikipedia

    en.wikipedia.org/wiki/Icositetragon

    As 24 = 2 3 × 3, a regular icositetragon is constructible using an angle trisector. [1] As a truncated dodecagon , it can be constructed by an edge- bisection of a regular dodecagon. Symmetry

  9. Heron's formula - Wikipedia

    en.wikipedia.org/wiki/Heron's_formula

    If ⁠ ⁠ is the radius of the incircle of the triangle, then the triangle can be broken into three triangles of equal altitude ⁠ ⁠ and bases ⁠, ⁠ ⁠, ⁠ and ⁠. ⁠ Their combined area is A = 1 2 a r + 1 2 b r + 1 2 c r = r s , {\displaystyle A={\tfrac {1}{2}}ar+{\tfrac {1}{2}}br+{\tfrac {1}{2}}cr=rs,} where s = 1 2 ( a + b + c ...