Area of a Circle

Area of a Circle

• The area A of a circle equals the product of π and the square of its radius r.

• When finding the area of a circle, you have to use the button on your calculator.

• You can not use an approximation of .• Do not use 3.14 for pi.

Example 1

Find the area of the circle. Round your answer to the nearest hundredth.

2 in.

You can not use the approximation 3.14 for pi because it won’t give you the same rounded answer.

The area of the circle is 12.57 square inches.

PEMDAS – you solve exponents first before you multiply by pi

2rA 2rA 22A4A

...5663706.12A57.12A

2)2(14.3A)4(14.3A

56.12A

Example 2

Find the area of the circle. Round your answer to the nearest hundredth.

28 cm.You are given the diameter, but you will need to find out what the radius is to use the area formula.

2rA 2

dr

2

28r

14r

214A

196A...7521601.615A

75.615A

The area of the circle is 615.75 square centimeters.

Example 3

Find the area of the face of the Virginia quarter with a diameter of 24 millimeters. Round your answer to the nearest hundredth.

2rA 2

dr

2

24r

12r

212A

144A...3893421.452A

39.452A 2mm

The area of the Virginia quarter is 452.39 .2mm

Practice Problems1. Find the area of a circle with a radius of 3.2

centimeters. Round your answer to the nearest hundredth.

2. The bottom of a circular swimming pool with a diameter of 30 feet is painted blue. How many square feet are blue? Round your answer to the nearest hundredth.

2rA 22.3A24.10A

...16990877.32A

17.32AThe area of the circle is 32.17 .

2cm

2cm

2rA

2

dr

2

30r

15r

215A225A

......8583471.706A86.706A 2ft

The area of the circle is 706.86 .

2ft