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Area of Circles and Parts of Circles. Finding the area of a circle The area of a circle is found using the formula A =  r 2.

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Presentation on theme: "Area of Circles and Parts of Circles. Finding the area of a circle The area of a circle is found using the formula A =  r 2."— Presentation transcript:

1 Area of Circles and Parts of Circles

2 Finding the area of a circle The area of a circle is found using the formula A =  r 2

3 Practice Finding the area of a circle A =  r 2 A =  (2.17) 2 A =  cm 2 or cm 2

4 Practice Finding the area of a circle A =  r 2 A =  (5.19/2) 2 A =  cm 2 or cm 2

5 Practice Finding the area of a circle 6 3 Find the area of the shaded region A = 36  - 9  = 27  u 2 or u 2

6 Practice Finding the area of a circle Find the area of the circle if the area of the square = 144 m 2 The circle has a diameter of 12 m so A = 36  m 2 or m 2

7 Practice Finding the area of a circle Find the area of the shaded region if the side of the square = 10 cm The area is 100 cm  cm 2 or cm 2

8 Practice Finding the area of a circle Find the area of the shaded region if the side of the square is 12 cm. The area is 144 cm 2 - 4(9  ) cm 2 or 30.9 cm 2

9 Finding the radius when area is known Since the formula for the area of a circle is A = πr 2, the radius can be determined if the area is known. If A = 49π, then r 2 = 49. If r 2 = 49, then r = 7.

10 Finding the radius when area is known Find the radius for each circle 1. A = 144π 2. A = 36π 3. A = 81π 4. A = 25π 5.A = 100π r = 12 r = 6 r = 9 r = 5 r = 10

11 Finding the circumference when area is known To find the circumference when the area is known, first find the radius and then use it to find the circumference. A = 49π so r = 7 and d = 14 C = 14 π

12 Finding the circumference when area is known Find the circumference for each circle 1. A = 144π 2. A = 36π 3. A = 81π 4. A = 25π 5.A = 100π C = 24π C = 12π C = 18π C = 10π C = 20π

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