Geometry/Circles/Radii, Chords and Diameters

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A circle is a set of all points in a plane that are equidistant from a single point; that single point is called the centre of the circle and the distance between any point on circle and the centre is called radius of the circle.


a chord is an internal segment of a circle that has both of its endpoints on the circumference of the circle.

  • the diameter of a circle is the largest chord possible


a secant of a circle is any line that intersects a circle in two places.

  • a secant contains any chord of the circle


a tangent to a circle is a line that intersects a circle in exactly one point, called the point of tangency.

  • at the point of tangency the tangent line and the radius of the circle are perpendicular