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central angle

an angle whose vertex is the center of the circle.

minor arc

part of a circle that measures less than 180 degrees

major arc

part of a circle that measures between 180 degrees and 360 degrees

semicircle

an arc whose endpoints are half the circle; endpoints are the diameter of the circle.

congruent arcs

2 arcs of the same circle or of congruent circles that have the same measure.

inscribed angle

and whose vertex is on a circle and whose sides contain chords of the circle

interepted arc

the arc that lies in the interior of an inscribed angle and has endpoints on the angle.

inscribed polygon

polygon whose vertices all lie on a circle.

circumscribed circle

circle with an inscribed polygon

circle

set of all points in a plane that are equidistant from a given point

radius

distance from the center of a circle to a point on the circle

congruent circles

2 circles that have the same radius

diameter

chord that passes through the center of a circle

chord

segment whose endpoints are points on the circle

secant

segment that intersects a circle twice.

tangent circles

circles that intersect in one point

concentric

circles that have a common center

common tangent

a line or segment that is tangent to 2 circles

interior of a circle

all points of the plane that are inside a circle

exterior of a circle

all points of the same plane that are outside a circle

point of tangency

point where tangent line meets circle line