# Chapter 10 Vocabulary – Properties of Circles

Word Definition
center of a circle see circle
central angle an angle whose vertex is the center of the circle
chord a segment whose endpoints are on a circle
circle the set of all points in a plane that are equidistant from a given point called the center of the circle
circumscribed circle the circle that contains the vertices of an inscribed polygon
congruent arcs two arcs that have the same measure and are arcs of the same circle or of congruent circles
congruent circles two circles that have the same radius
diameter of a circle a chord that passes through the center of a circle; the distance across a circle through its center
external segment the part of a secant segment that is outside the circle
inscribed angle an angle whose vertex is on a circle and whose sides contain chords of the circle
inscribed circle a polygon whose vertices all lie on a circle
intercepted arc the arc that lies in the interior of an inscribed angle and has endpoints on the angle
major arc part of a circle that measures between 180 degrees and 360 degrees
measure of a major arc the difference between 360 degrees and the measure of the related minor arc
measure of a minor arc the measure of the arc's central angle
minor arc part of a circle that measures less than 180 degrees
radius a segment whose endpoints are the center of the circle and a point on the circle; the distance from the center of a circle to any point on the circle; plural radii
secant line a line that intersects a circle in two points
secant segment a segment that contains a chord of a circle and has exactly one endpoint outside the circle
segments of a chord when two chords intersect in the interior of a circle, each chord is divided into two segments called segments of the chord
semicircle an arc with endpoints that are the endpoints of a diameter of a circle; the measure of a semicircle is 180 degrees
standard equation of a circle the standard equation of a circle with center (h, k) and radius r is (x – h) squared + (y – k) squared = r squared
tangent line a line in the plane of a circle that intersects the circle in exactly one point, the point of tangency