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Chapter 10. Properties of Circles. 10.1 Using Properties of Tangents. Circle- a set of all points in a plane that are equidistant from a given point called the center. Radius- a segment whose endpoints are the center and any point on the circle Chord- a segment whose endpoints are on a circle
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Chapter 10 Properties of Circles
10.1 Using Properties of Tangents • Circle- a set of all points in a plane that are equidistant from a given point called the center
Radius- a segment whose endpoints are the center and any point on the circle • Chord- a segment whose endpoints are on a circle • Diameter- a chord that contains the center of the circle • Secant- a line that intersects a circle in two points • Tangent- a line in the plane of a circle that intersects the circle in exactly one point
Can you name it? • Chord • Radius • Diameter • Secant • Tangent • Point of Tangency
Coplanar circles • Concentric circles • Internally tangent circles • Externally tangent circles
Common tangents • Internal common tangent • External common tangent
Theorems • In a plane, a line is tangent to a circle if and only if the line is perpendicular to a radius of the circle at its endpoint on the circle
Tangent segments from a common external point are congruent.
Examples • Is segment BC tangent to circle A if segment AB is a radius?
Example • S is a point of tangency. Find r.
Example • Point R and T are tangent to circle P. Find x.
Example • How many common tangents?
10.2 Finding Arc Measures • Central angle- an angle whose vertex is the center of the circle • Major arc • Minor arc • Semicircle
Arc Addition Postulate • The measure of an arc formed by two adjacent arcs is the sum of the measures of the two arcs.
Congruent Circles and Arcs • Two circles are congruent if they have the same radius. • Two arcs are congruent if they have the same measure and they are arcs of the same circle or of congruent circles. • The radii of a circle, or of congruent circles, are congruent.
Example • Are arcs AB and DE congruent?
Example • Ages of people in a town (in years)
10.3 Applying Properties of Chords • In the same circle, or in congruent circles, two minor arcs are congruent if and only if their corresponding chords are congruent.
If one chord is a perpendicular bisector of another chord, then the first chord is a diameter. • If the diameter of a circle is perpendicular to a chord, then the diameter bisects the chord and its arc.
In the same circle, or in congruent circles, two chords are congruent if and only if they are equidistant from the center.
Example • BC= 2x +6 • ED = 3x – 1 • Find BC
Example • Three props are placed on a stage (P,Q,R). Where do you put the table so that it is the same distance from each prop?