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Circles. 3/30/09. Circle. Definition A circle is the set of all points in a plane that are equidistant from a given point in the plane known as the center of the circle. How do we represent a circle. Parts of A Circle. Radius
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Circles 3/30/09
Circle • Definition • A circle is the set of all points in a plane that are equidistant from a given point in the plane known as the center of the circle. • How do we represent a circle
Parts of A Circle • Radius • A segment from the center of the circle to a point on the circle.
What can we say about all the radii of a circle? • They are all equal! 8
Parts of a Circle • CHORD • Is a segment whose endpoints lie on a circle.
Parts of a Circle • Diameter • Is a chord that contains the center of a circle.
Diameter/Radius • What do we know about the radius of a circle and its diameter? • The diameter is TWICEthe radius.
Parts of a Circle • Arc • An unbroken part of a circle. • Any two distinct points on a circle divide the circle into two arcs. • Endpoints • The two distinct points of the arcs
Parts of a Circle • Semicircle • An arc whose endpoints are endpoints of a diameter. • Also known as a “half-circle”
Parts of a Circle • Minor Arc • Is an arc that is shorter than a semicircle of that circle • Major Arc • Is an arc that is longer than a semicircle of that circle.
Parts of a Circle • Central Angle • It is an angle whose vertex is the center of the circle.
Degree Measures of Arcs • The degree measure of a MINOR ARC is the measure of its central angle.
Degree Measures of Arcs • The degree measure of a major arc is 360o minus the degree measure of its minor arc.
Degree Measures of Arcs • The degree measure of a semicircle is 180o
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:
Class Work • WS • 9.1
Homework • Page 570 • 11-19