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Perimeter and Area with Circles. Circumference of a Circle Circumference is the perimeter of the circle Formula: or (for exact answers, leave π in your.

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Presentation on theme: "Perimeter and Area with Circles. Circumference of a Circle Circumference is the perimeter of the circle Formula: or (for exact answers, leave π in your."— Presentation transcript:

1 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 Radian Measure Radian measure is the arc length in the unit circle (a circle with radius of 1)

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

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

9 Shortcut Since 90° is 1/4 th of the circle, you can find the circumference and divide it by 4. C = 12 π Arc = 12 π /4 = 3 π cm

10 Example Convert 90° to radians. Convert 150° to radians. Convert 315° to radians (answers on the next slide)

11 Answers

12 Area of a circle Formula:

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

14 Example Find the Area of the Circle Radius = 20 cm cm 2

15 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

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


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