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  2. Regular polygon - Wikipedia

    en.wikipedia.org/wiki/Regular_polygon

    Some regular polygons are easy to construct with compass and straightedge; other regular polygons are not constructible at all. The ancient Greek mathematicians knew how to construct a regular polygon with 3, 4, or 5 sides, [20]: p. xi and they knew how to construct a regular polygon with double the number of sides of a given regular polygon.

  3. Polygon - Wikipedia

    en.wikipedia.org/wiki/Polygon

    The area of a regular polygon is given in terms of the radius r of its inscribed circle and its perimeter p by =. This radius is also termed its apothem and is often represented as a. The area of a regular n-gon in terms of the radius R of its circumscribed circle can be expressed trigonometrically as: [12] [13]

  4. List of second moments of area - Wikipedia

    en.wikipedia.org/wiki/List_of_second_moments_of_area

    Regular polygons; Description Figure Second moment of area Comment A filled regular (equiliteral) triangle with a side length of a = = [6] The result is valid for both a horizontal and a vertical axis through the centroid, and therefore is also valid for an axis with arbitrary direction that passes through the origin.

  5. Constructible polygon - Wikipedia

    en.wikipedia.org/wiki/Constructible_polygon

    A regular polygon with n sides can be constructed with ruler, compass, and angle trisector if and only if =, where r, s, k ≥ 0 and where the p i are distinct Pierpont primes greater than 3 (primes of the form +). [8]: Thm. 2 These polygons are exactly the regular polygons that can be constructed with Conic section, and the regular polygons ...

  6. Shoelace formula - Wikipedia

    en.wikipedia.org/wiki/Shoelace_formula

    Shoelace scheme for determining the area of a polygon with point coordinates (,),..., (,). The shoelace formula, also known as Gauss's area formula and the surveyor's formula, [1] is a mathematical algorithm to determine the area of a simple polygon whose vertices are described by their Cartesian coordinates in the plane. [2]

  7. Pentagon - Wikipedia

    en.wikipedia.org/wiki/Pentagon

    The area of any regular polygon is: = where P is the perimeter of the polygon, and r is the inradius (equivalently the apothem). Substituting the regular pentagon's ...

  8. Area of a circle - Wikipedia

    en.wikipedia.org/wiki/Area_of_a_circle

    The area of a regular polygon is half its perimeter multiplied by the distance from its center to its sides, and because the sequence tends to a circle, the corresponding formula–that the area is half the circumference times the radius–namely, A = ⁠ 1 / 2 ⁠ × 2πr × r, holds for a circle.

  9. Method of exhaustion - Wikipedia

    en.wikipedia.org/wiki/Method_of_exhaustion

    The quotients formed by the area of these polygons divided by the square of the circle radius can be made arbitrarily close to π as the number of polygon sides becomes large, proving that the area inside the circle of radius r is πr 2, π being defined as the ratio of the circumference to the diameter (C/d).