Circle – the set of all points in a plane agiven distance away from a center point. A circle is named by its center point. For A example: Circle A or A. Radius (r) Plural: RadiiRadius – the “given distance away fromthe center point” of a circle; a segment that joins the center to a point on the circle.
Sphere – the set of all points a given distance away from a center point.
Chord – a segment whose endpoints lie on on the circle. Example: DC A B C D Diameter – a chord that passes through the center of the circle. Example: ABA diameter is twice the length of a radius.
Secant – a line that contains a chord. B Example: AB A **Note: A chord and a secant can be namedusing the same letters. The notation tells youwhether it is a secant or a chord. A secant is a line; a chord is a segment.** Secant: AB Chord: AB
Tangent – a line that intersects a circle at exactly one point. Not a B tangent! A The point at which the circle and the tangent intersect is called the point of tangency.Example: AB Example: A
5cm Congruent Circles – circles with5cm congruent radii. ConcentricCircles – circles with the same center point.
A polygon is inscribed in a circleand the circle is circumscribedabout the polygon when all ofthe vertices of the polygon lieon the circle. This pentagon is inscribed inside of the circle.
When each side of a polygon istangent to a circle, the circle issaid to be inscribed in thepolygon. This circle is inscribed inside of the pentagon.