How can you find the circumference of a circle if you only know the area?

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# How can you find the circumference of a circle if you only know the area? - PowerPoint PPT Presentation

How can you find the circumference of a circle if you only know the area?. For Example. A circle has an area 16 π cm 2 . What is the circumference of the circle?. In this lesson you will learn how to find the circumference of a circle by using the measure of area. Area of a Circle = π r 2.

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Presentation Transcript

For Example

A circle has an area 16πcm2. What is the circumference of the circle?

In this lesson you will learn how to find the circumference of a circle by using the measure of area.

Area of a Circle = πr2

Circumference of a Circle= πdor 2πr

Finding the square root of a number is not the same as dividing it by 2.

Correct

Wrong

= 8

= 4

Bill has a circular garden that he wants to put a fence around. He knows that the area of a garden is 16π yds2. How much fencing does Bill need to go around the circumference of the garden?

A = πr2

C = 2πr

A = 16πyds2

C = 2π(4 yds)

r2 = 16 yds2

4 yds

C = 8πyds

r = 4 yds

A circle has an approximate area of 28.26 ft2. If 3.14 was used for pi, what is the circumference of the circle?

A = πr2

C = 2πr

28.26ft2 = 3.14r2

3.14 3.14

C = 2(3.14)3

C = 18.84 ft

9ft2 = r2

3 ft = r

In this lesson you have learned how to find the circumference of a circle by using the measure of the area.

The area of a circle is 16πmeters2. Stephanie concluded that the circumference of the circle would be 16π. She stated “the radius would be 8 meters since the square root of 16 is 8.” What mistake did Stephanie make. Write an explanation describing how to fix her mistake.

A circle inside of a square touches the square at each edge as shown below. If the circle has an area of 25π feet2, find the area of the square.

A circle has an area of 113.04 cm2. What is the circumference of the circle?