circle
the set of all points that are the same distance away from a fixed point (the center)
radius
the distance between the center of a circle and a point on the circle
chord
a segment on the interior of a circle with endpoints on the circle
diameter
a type of chord that passes through the center of the circle
circumference
the distance around the circle from one point back to the same point
arc
one section of the circumference of a circle
minor arc
an arc measuring less than 180°
major arc
An arc measuring more than 180°
arc length
the distance between two points on the circle
secant
a line that passes through a circle, intersecting it at two distinct points
tangent
a line that intersects the circle in exactly one point
point of tangency
the point where the tangent intersects the circle
concentric circles
two circles that share a common center
central angle
an angle on the interior, or inside, of a circle with its vertex at the circle's center
intercepted arc
the arc created by the endpoints of the angle
semicircle
an arc where the central angle is created by a diameter of the circle
adjacent arcs
arcs that share a common point
arc addition postulate
the measure of an arc created by two adjacent arcs may be found by adding the measures of the two adjacent arcs
nonadjacent arcs
arcs that do not have a common point on the circumference of a circle
congruent arcs theorem
two arcs are congruent if the central angles that intercept them are also congruent
inscribed angle
an angle is in the interior of a circle and its vertex is a point on the circle
interior intersecting chords theorem
the measure of an angle created by chords, secants, or a combination on the interior of a circle is equal to half the sum of the arcs it and its vertical angle intercept
inscribed angle theorem
the measure of an inscribed angle is equal to half the measure of its intercepted arc
secant-tangent intersection theorem
when a secant and tangent intersect at the point of tangency, the angles created at the point of intersection are half the measurement of the arcs they intersect
exterior angle to a circle theorem
If two secants, two tangents, or a secant and a tangent intersect outside a circle, the measure of the created angle between them is one-half the absolute value of the difference of the measures of their intercepted arcs