2.  A circle is defined by it’s center and all points equally distant from that center.  You name a circle according to it’s center point.  The radius of a circle is the distance from it’s center to any point on the circle.  A chord is a segment whose endpoints lie on the circle.

3.  The diameter of circle is twice the radius.  The diameter is the longest chord.

4.  A tangent is a line that touches the circle at only one point.  A secant is a lines that passes through the circle touching it in exactly two points.  Line AB is a secant line.  Line CD is a  tangent line.

5.  A central angle is an angle whose vertex is at the center of the circle.  is a central angle

6.  The measure of a minor arc is equal to the measure of its central angle.  A minor arc measures less than 180°  When naming a minor arc, we use two letters and the arc symbol.  For example minor arc AB, we use the notation

7.  A major arc measures more than 180  It’s measure is 360 – the minor arc  When naming a it you must use 3 points on the arc to show it is major along with the arc symbol.  For example, major arc ADB is noted

8.  A semicircle is half the circle. Its endpoints are the endpoints of a diameter.  You must use three letters to name a semicircle.

9.  When talking about the degree measure of an arc, we use the notation

10.  The measure of an arc formed by two adjacent arcs is the sum of the measures of the two arcs

12.  Congruent circles have the same radius.  Congruent arcs have the same measure and lie in the same circle or congruent circles.

14.  The tangent of a circle is perpendicular to the radius at the point of tangency.

16.  Tangent segments from a common external point are congruent.

18.  In the same circle, or in congruent circles, two minor arcs are congruent if and only if their corresponding chords are congruent.

19.  The diameter of a circle is perpendicular to a chord iff the diameter bisects the chord and its arc.

21.  In the same circle, or in congruent circles, two chords are congruent iff they are equidistant from the center.

23.  An inscribed angle is an angle whose vertex is on a circle.  An Intercepted arc is the arc in the interior of the angle.

24.  The measure of an inscribed angle is half the measure of its intercepted arc.

27.  A polygon is an inscribed polygon if all of its vertices lie on a circle.  The circle that contains the vertices is circumscribed circle.

28.  A quadrilateral can be inscribed in a circle if and only if its opposite angles are supplementary.