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Parts of a Circle

Parts of a Circle. 9.1 cm. 21 km. 4 cm. 13.8 cm. 9 km. Simplify . 4 2 (5)(3) 2 29 – 5 2 Calculate the area. Circle : The set of all points the same distance from a point called the center. Center : The middle of a circle.

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Parts of a Circle

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  1. Parts of a Circle

  2. 9.1 cm 21 km 4 cm 13.8 cm 9 km Simplify. • 42 • (5)(3)2 • 29 – 52 Calculate the area.

  3. Circle: • The set of all points the same distance from a point called the center. • Center: The middle of a circle. • Radius: The distance from the center of a circle to any point on the edge. • Chord: A line segment with endpoints on the circle. • Diameter: The distance across a circle through the center.

  4. Central Angle: An angle with its vertex at the center of the circle.

  5. Videos ~ SAV Lesson 3 ~ Parts of circle • animated characters: http://www.youtube.com/watch?v=eiHWHT_8WrE&NR=1 • Kids: http://www.youtube.com/watch?v=nIQo_-VVNEQ&NR=1

  6. Example 1 Use C to name each circle part. A chord • AB or EF A radius • CD or CE or CF A diameter • EF Central Angle • ∠ECD or ∠FCD or ∠FCE

  7. Example 2 The diameter of a circle is 12 centimeters. Find the radius. • Radius is half the diameter. 12 ÷ 2 = 6 • The radius is 6 cm. The radius of a circle is 7 inches. Find the diameter. • Diameter is double the radius. 7•2 = 14 • The diameter is 14 inches.

  8. Example 3 Find the measure of the missing central angle. • The sum of the central angles is 360. • Write an equation. 140 + 40 + 100 + x = 360 • Combine like terms. 280 + x = 360 • Subtract. –280 – 280x = 80 • The missing central angle , x, is 80⁰.

  9. How many degrees are in a circle? • Name the longest chord in A. • Draw M with radius AM, diameter PR and chord XY.

  10. Communication Prompt • Why is the diameter the longest chord in a circle? • Why is proper notation important?

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