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  2. Cyclic quadrilateral - Wikipedia

    en.wikipedia.org/wiki/Cyclic_quadrilateral

    In Euclidean geometry, a cyclic quadrilateral or inscribed quadrilateral is a quadrilateral whose vertices all lie on a single circle. This circle is called the circumcircle or circumscribed circle , and the vertices are said to be concyclic .

  3. Japanese theorem for cyclic quadrilaterals - Wikipedia

    en.wikipedia.org/wiki/Japanese_theorem_for...

    Then the quadrilateral formed by M 1, M 2, M 3, M 4 is a rectangle. Proofs are given by Bogomolny [2] and Reyes. [1] This theorem may be extended to prove the Japanese theorem for cyclic polygons, according to which the sum of inradii of a triangulated cyclic polygon does not depend on how it is triangulated. The special case of the theorem for ...

  4. Japanese theorem for cyclic polygons - Wikipedia

    en.wikipedia.org/wiki/Japanese_theorem_for...

    In geometry, the Japanese theorem states that no matter how one triangulates a cyclic polygon, the sum of inradii of triangles is constant. [1]: p. 193 Conversely, if the sum of inradii is independent of the triangulation, then the polygon is cyclic. The Japanese theorem follows from Carnot's theorem; it is a Sangaku problem.

  5. Miquel's theorem - Wikipedia

    en.wikipedia.org/wiki/Miquel's_theorem

    The theorem (and its corollary) follow from the properties of cyclic quadrilaterals. Let the circumcircles of A'B'C and AB'C' meet at M ≠ B ′ . {\displaystyle M\neq B'.} Then ∠ A ′ M C ′ = 2 π − ∠ B ′ M A ′ − ∠ C ′ M B ′ = 2 π − ( π − C ) − ( π − A ) = A + C = π − B , {\displaystyle \angle A'MC'=2\pi ...

  6. Ptolemy's theorem - Wikipedia

    en.wikipedia.org/wiki/Ptolemy's_theorem

    This is not a cyclic quadrilateral. The equality never holds here, and is unequal in the direction indicated by Ptolemy's inequality. The equation in Ptolemy's theorem is never true with non-cyclic quadrilaterals. Ptolemy's inequality is an extension of this fact, and it is a more general form of Ptolemy's theorem.

  7. Brahmagupta theorem - Wikipedia

    en.wikipedia.org/wiki/Brahmagupta_theorem

    In geometry, Brahmagupta's theorem states that if a cyclic quadrilateral is orthodiagonal (that is, has perpendicular diagonals), then the perpendicular to a side from the point of intersection of the diagonals always bisects the opposite side. [1] It is named after the Indian mathematician Brahmagupta (598-668). [2]

  8. Brahmagupta's formula - Wikipedia

    en.wikipedia.org/wiki/Brahmagupta's_formula

    In Euclidean geometry, Brahmagupta's formula, named after the 7th century Indian mathematician, is used to find the area of any convex cyclic quadrilateral (one that can be inscribed in a circle) given the lengths of the sides. Its generalized version, Bretschneider's formula, can be used with non-cyclic quadrilateral.

  9. Dividing a circle into areas - Wikipedia

    en.wikipedia.org/wiki/Dividing_a_circle_into_areas

    The number of points (n), chords (c) and regions (r G) for first 6 terms of Moser's circle problem. In geometry, the problem of dividing a circle into areas by means of an inscribed polygon with n sides in such a way as to maximise the number of areas created by the edges and diagonals, sometimes called Moser's circle problem (named after Leo Moser), has a solution by an inductive method.