9.1+(WiBr56)

__Vocabulary__
 * radius**- is a segment from the center of the circle to a point on the circle
 * chord**- is a segment whose endpoints line in a circle
 * diameter**- is a chord that contains the center of a circle.
 * Arc**- an unbroken part of a circle.
 * endpoints**- the points on the arcs
 * semicircle**- is an arc whose endpoints are endpoints of a diameter. (half a circle)
 * minor arc**- an arc that is shorter than a semicircle of the circle.
 * major arc**- an arc that is longer than a semicircle of that circle.
 * central angle**- a circle is an angle in a the plane of a circle whose vertex is the center of the circle
 * intercepted arc**- An arc whose endpoints lie on the sides of the angle and whose other points lie in the interior of the angle

__Definition: Circle__ A circle is the set of all points in a plane that are equidistant from a given point in the plan known as the center of a circle. A radius is a segment from the center of the circle to a point on the circle. A chord is a segment whose endpoints line in a circle. A diameter is a chord that contains the center of a circle.

__Definition: Central Angle and Intercepted Arc__ A central angle of a circle is an angle in a plane of a circle whose vertexis the center of the circle. An arc whose endpoints lie on the sides of the angle and whose other points lie in the interior of the angle is the intercepted arc of the central angle.

__Definition: Degree Measure of Arcs__ The degree measure of a minor arc is the measure of its central angle. The degree measure of a major arc is 360 degrees minus the degree measure of its minor arc. The degree measure of a semicircle is 180 degrees.

__Arc Length__ If r is the radius of a circle and M is the degree measure of an arc of the circle, then the length, L, of the arc is given by the following: L= M / 360 degrees (2 pie r)

__Chords and Arcs Theorem__ In a circle, or congruent circles, the arcs of congruent chords are congruent.

__The Converse of the Chords and the Arcs Theorem__ In a circle or in congruent circles, the chords of congruent arcs are congruent.

[[image:http://farm1.static.flickr.com/158/375609485_c53b997b7c_m.jpg width="240" height="230" link="http://www.flickr.com/photos/aekeith2/375609485/"]]
__Example__ L=m/360 degrees x 2 (pie) r measure of angle W 80 degrees; radius 20 L= (80 degrees) / 360 degrees x 2 pie (20) L= 27.93
 * Find the Measure of an Arc with the given central angle measure, m angle W, in a circle with radius r.**