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  2. Thales's theorem - Wikipedia

    en.wikipedia.org/wiki/Thales's_theorem

    As stated above, Thales's theorem is a special case of the inscribed angle theorem (the proof of which is quite similar to the first proof of Thales's theorem given above): Given three points A, B and C on a circle with center O, the angle ∠ AOC is twice as large as the angle ∠ ABC. A related result to Thales's theorem is the following:

  3. Conway circle theorem - Wikipedia

    en.wikipedia.org/wiki/Conway_circle_theorem

    Conway's circle theorem as a special case of the generalisation, called "side divider theorem" (Villiers) or "windscreen wiper theorem" (Polster)) Conway's circle is a special case of a more general circle for a triangle that can be obtained as follows: Given any ABC with an arbitrary point P on line AB.

  4. Inscribed angle - Wikipedia

    en.wikipedia.org/wiki/Inscribed_angle

    As a consequence of the theorem, opposite angles of cyclic quadrilaterals sum to 180°; conversely, any quadrilateral for which this is true can be inscribed in a circle. As another example, the inscribed angle theorem is the basis for several theorems related to the power of a point with respect to a circle. Further, it allows one to prove ...

  5. Circle theorem - Wikipedia

    en.wikipedia.org/wiki/Circle_theorem

    Circle theorem may refer to: Any of many theorems related to the circle; often taught as a group in GCSE mathematics. These include: Inscribed angle theorem. Thales' theorem, if A, B and C are points on a circle where the line AC is a diameter of the circle, then the angle ∠ABC is a right angle. Alternate segment theorem. Ptolemy's theorem.

  6. Pascal's theorem - Wikipedia

    en.wikipedia.org/wiki/Pascal's_theorem

    A short elementary proof of Pascal's theorem in the case of a circle was found by van Yzeren (1993), based on the proof in (Guggenheimer 1967). This proof proves the theorem for circle and then generalizes it to conics. A short elementary computational proof in the case of the real projective plane was found by Stefanovic (2010).

  7. Gershgorin circle theorem - Wikipedia

    en.wikipedia.org/wiki/Gershgorin_circle_theorem

    Whichever continuity is used in a proof of the Gerschgorin disk theorem, it should be justified that the sum of algebraic multiplicities of eigenvalues remains unchanged on each connected region. A proof using the argument principle of complex analysis requires no eigenvalue continuity of any kind. [1] For a brief discussion and clarification ...

  8. Nine-point circle - Wikipedia

    en.wikipedia.org/wiki/Nine-point_circle

    A nine-point circle bisects a line segment going from the corresponding triangle's orthocenter to any point on its circumcircle. Figure 4. The center N of the nine-point circle bisects a segment from the orthocenter H to the circumcenter O (making the orthocenter a center of dilation to both circles): [6]: p.152

  9. Tangent lines to circles - Wikipedia

    en.wikipedia.org/wiki/Tangent_lines_to_circles

    In Euclidean plane geometry, a tangent line to a circle is a line that touches the circle at exactly one point, never entering the circle's interior.Tangent lines to circles form the subject of several theorems, and play an important role in many geometrical constructions and proofs.