Circumferences and Areas of Circles Unit 11 Section 5 Know and use the formula for the circumferences and areas of circles.

Area of a Circle Area = п · ( radius) ² radius Circumference of Circle Circumference = 2 п( radius) or Circumference = п( diameter) radius diameter

Example 1: Complete the table. Leave the answers in terms in п Practice: Lesson 11.5 Notes #1-4 rdCA п 100 п

Guided Practice: For questions A-C, the radius of ⊙ O is three times the radius of ⊙ R. A.What is the ratio of the circumference to the diameter for each circle? B.Compare the circumferences of the two circles. C.Compare the area of the two circles

Circle Challenge Problems Example 2: A school’s wrestling mat is a square with 40 ft sides. A circle 28 ft in diameter is painted on the mat. No wrestling is allowed outside the circle. Find the area of the part of the mat that is not used for wrestling. Give your answer to the nearest square foot. Practice: Lesson 11.5 Notes #5 Example 3: If a bicycle tire ha a diameter of 26 in., how does it travel in 1000 revolutions of the tire. Give your answer to the nearest in. Practice: Lesson 11.5 Notes #6

Example 4: Find the area of the shaded region Practice: Lesson 11.5 Notes #7-8