10.4 area of a circle

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1

10.4 ­ Area of a Circle

Joseph WilliamsGESDjwilliams@gesd40.org

Objective: Find the area of a circle.

2

Radius ­ The distance from the center of a circle to any point on the circle.

Image: '1917 D penny'www.flickr.com/photos/96586445@N00/188729710

3

pi ­  the ratio of the circumference of a circle to its diameter. ( 3.14 )

Image: 'Happy 3.14 Day3'www.flickr.com/photos/17731548@N00/421636858

4

Area of a Circle

Area = (pi)(radius)2

A =      r2 A = (3.14)r2

3 cmA = (3.14)32

A = 3.14    9A = 28.26 cm2

5

Find the area of the key and half circle above the free throw line.

12 ft.

19 ft.

6 ft

6

Area of the keyA = bh

A = 19   12 = 228 ft2

Area of the half circleA =     r2

A = 3.14   62  = 3.14   36 = 113.04 ft2

We only need the area for half the circle!

113.04 / 2 = 56.52 ft2 

Now we need to add them.

228 + 56.52 =

284.52 ft2

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