Chapter 9 -- Circles 9-1 Basic Terms Vocabulary: Circle: the set of points in a plan at a given distance from a given point in that plane • Center: the given point • Radius: (plural is radii pronounced "ray-dee-eye") the given distance. Any segment that joins the center to a point on the circle is a radius of the circle. The radius is the distance. • Chord: a segment whose endpoints line on a circle • Secant: a line that contains a chord • Diameter: a chord that contains the center of the circle. The diameter is the measurement; a diameter is any chord that contains the center of the circle. • Tangent: a line in the plane of a circle that intersects the circle in exactly one point, called the point of tangency. • Sphere: with center O and radius r, is the set of all points in space at a distance r from point O. Spheres also have diameter, chord, secant, and tangent. • Congruent Circles (or Spheres): circles or spheres with congruent radii. • Concentric Circles: circles that lie in the same plane and have the same center. • • Concentric Spheres: spheres that have the same center. • Inscribed Polygons: a polygon that is inside of a circle and whose vertices touch the circle. • Circumscribed Circles: a circle that is on the outside of a polygon whose vertices touch the circle. 2.29.12 Friday, February 24, 2012 9:08 AM H Geom - 1 Page 1