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# 14 2 tangents to a circle lesson

## on Jul 11, 2013

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## 14 2 tangents to a circle lessonPresentation Transcript

• Use Properties of Tangents 14-2
• Vocabulary • Circle- the set of all pts in a plane that are equidistant from a given pt. called the center of the circle. • Radius- segment whose endpoints are the center and any point on the circle • Diameter- a chord that contains the center of the circle. • Two polygons are similar if corresponding angles are congruent and corresponding side lengths are proportional. ΔABC ∼ ΔDEF
• P P is the center of the circle A B Segment AB is a diameter C Segments AP, PB, and PC are radii
• Chord • Chord- a segment whose endpoints are on the circle. A B
• Secant • Secant- a line that intersects a circle in 2 pts A B
• Tangent • Tangent- a line in the plane of the circle that intersects the circle in exactly one point, called the point of tangency.
• • Point of tangency- point where tangent intersects a circle TPoint T is the point of tangency
• Example tell whether the segment is best described as a chord, secant, tangent, diameter or radius • Segment AH • Segment EI • Segment DF • Segment CE A B C D E F G H I
• Example tell whether the segment is best described as a chord, secant, tangent, diameter or radius • Segment AH • Segment EI • Segment DF • Segment CE A B C D E F G H I tangent Diameter Chord radius
• Tangent circles- circles that intersect in one point Concentric circles- circles that have a common center but different radii lengths
• Common internal tangent- a tangent that intersects the segment that connects the centers of the circles Common external tangent- does not intersect the segment that connects centers
• Example Common internal or external tangent?
• Example Common internal or external tangent? external
• Theorem 14-4 • In a plane, a line is tangent to a circle if and only if it is perpendicular to a radius of the circle at its endpoint on the circle.
• Example Is segment CE tangent to circle D? Explain D E C 11 45 43 Remember in order to find if a line is tangent we need to know if there is a 90 degree angle
• Example Is segment CE tangent to circle D? Explain D E C 11 45 43 112 +432 =452 121+1849=2025 1970=2050 NO Let’s use the Pythagorean Theorem
• Example solve for the radius, r A B C r r 28ft 14ft
• Example solve for the radius, r A B C r r 28ft 14ft r2 +282 =(r+14)2 r2 + 784=r2 + 28r+196 784=28r+196 588=28r 21=r
• Theorem 14-6 • Tangent segments from a common external point are congruent.
• Example segment AB is tangent to circle C at pt B. segment AD is tangent to circle C at pt D. Find the value of X C B D A x2 +8 44
• Example segment AB is tangent to circle C at pt B. segment AD is tangent to circle C at pt D. Find the value of X C B D A x2 +8 44 x2 +8=44 x2 =36 X=6