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

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.  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

6.  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

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

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

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

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

13.  A secant is a line that intersects a circle in two points.  A tangent is a line that intersects the circle in exactly one point. T ANGENT

14. Secant Chord Tangent

15.  A line, ray, or segment that is tangent to two coplanar circles is called a common tangent.

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

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

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

21.  If one chord is a perpendicular bisector of another chord, then the first chord is a diameter.

22.  If a diameter of a circle is perpendicular to a chord, then the diameter bisects the chord and its arc.

24.  In the same circle, or in congruent circles, two chords are congruent if and only if they are equidistant from the center.