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  2. Central angle - Wikipedia

    en.wikipedia.org/wiki/Central_angle

    Angle AOB is a central angle. A central angle is an angle whose apex (vertex) is the center O of a circle and whose legs (sides) are radii intersecting the circle in two distinct points A and B. Central angles are subtended by an arc between those two points, and the arc length is the central angle of a circle of radius one (measured in radians). [1]

  3. Inscribed angle - Wikipedia

    en.wikipedia.org/wiki/Inscribed_angle

    Equivalently, an inscribed angle is defined by two chords of the circle sharing an endpoint. The inscribed angle theorem relates the measure of an inscribed angle to that of the central angle intercepting the same arc. The inscribed angle theorem appears as Proposition 20 in Book 3 of Euclid's Elements. Note that this theorem is not to be ...

  4. Thales's theorem - Wikipedia

    en.wikipedia.org/wiki/Thales's_theorem

    Thales's theorem can also be used to find the centre of a circle using an object with a right angle, such as a set square or rectangular sheet of paper larger than the circle. [7] The angle is placed anywhere on its circumference (figure 1). The intersections of the two sides with the circumference define a diameter (figure 2).

  5. Tangent lines to circles - Wikipedia

    en.wikipedia.org/wiki/Tangent_lines_to_circles

    If = + is the distance from c 1 to c 2 we can normalize by =, =, = to simplify equation (1), resulting in the following system of equations: + =, + =; solve these to get two solutions (k = ±1) for the two external tangent lines: = = + = (+) Geometrically this corresponds to computing the angle formed by the tangent lines and the line of ...

  6. Circular points at infinity - Wikipedia

    en.wikipedia.org/wiki/Circular_points_at_infinity

    Converting this into a homogeneous equation and taking the set of all complex-number solutions gives the complexification of the circle. The two circular points have their name because they lie on the complexification of every real circle. More generally, both points satisfy the homogeneous equations of the type

  7. Circle - Wikipedia

    en.wikipedia.org/wiki/Circle

    The sum of the squared lengths of any two chords intersecting at right angles at a given point is the same as that of any other two perpendicular chords intersecting at the same point and is given by 8r 2 − 4p 2, where r is the circle radius, and p is the distance from the centre point to the point of intersection.

  8. Unit circle - Wikipedia

    en.wikipedia.org/wiki/Unit_circle

    In mathematics, a unit circle is a circle of unit radius—that is, a radius of 1. [1] Frequently, especially in trigonometry, the unit circle is the circle of radius 1 centered at the origin (0, 0) in the Cartesian coordinate system in the Euclidean plane. In topology, it is often denoted as S 1 because it is a one-dimensional unit n-sphere ...

  9. Apollonian circles - Wikipedia

    en.wikipedia.org/wiki/Apollonian_circles

    Every blue circle intersects every red circle at a right angle. Every red circle passes through the two points C, D, and every blue circle separates the two points. In geometry, Apollonian circles are two families of circles such that every circle in the first family intersects every circle in the second family orthogonally, and vice versa.