1. Sections 11.1-11.2 Perimeter and Area with Circles

2. Circumference of a Circle Circumference is the perimeter of the circle Formula: or (for exact answers, leave π in your answer, for estimates, use the π key)

3. Example Find the circumference of a circle with a radius of 16 inches. inches

4. Example Find the circumference of the given circle. C = π d C = π (10) cm C = 10 π cm

5. Arc length is the length, of a piece, of the circle. Use a proportion that related part to whole, one side is length, the other side is degree measure. arc length = arc measure circumference 360 Arc Length

6. Example In Circle P, find the length of arc AB C = 20 π or 13.96 cm

7. Example In Circle G, with diameter 12 cm, find the length of C = 12 π Arc = 3 π cm

8. Radian Measure Radian measure is the arc length in the unit circle (a circle with radius of 1) To change degrees to radians Multiply: degrees * ( π radians/180) To change radians to degrees Multiply: radians * (180/ π radians)

9. Example Convert 150° to radians. Convert 7 π /4 radians to degrees (answers on the next slide)

10. Answers

11. Area of a circle Formula:

12. Example Find the area of a circle with a radius of 10 mm. mm 2

13. Example Find the Area of the Circle Radius = 20 cm cm 2

14. Area of a Sector The area of a sector is the area of a wedge shaped piece of the circle. You use a proportion just like the one for arc length

15. Example Find the area of the shaded sector of Circle O with radius 30 cm (for circle) cm 2

16. Practice P. 602: 3-9, 15-21 ALL ODDS P. 610: 3-9, 15-17, 21-27 ALL ODDS