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How to calculate the area of a circle. It’s as easy as pi.
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How to calculate the area of a circle. Its as easy as pi.

Mar 26, 2015

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Autumn Rowe
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Page 1: How to calculate the area of a circle. Its as easy as pi.

How to calculate the area of a circle.

It’s as easy as pi.

Page 2: How to calculate the area of a circle. Its as easy as pi.

Let’s first make sure that we understand the difference

between circumference and area.

Page 3: How to calculate the area of a circle. Its as easy as pi.

The circumference of a circle is the perimeter of the circle.

Page 4: How to calculate the area of a circle. Its as easy as pi.

Imagine that the circle is straightening itself out.

Page 5: How to calculate the area of a circle. Its as easy as pi.
Page 6: How to calculate the area of a circle. Its as easy as pi.
Page 7: How to calculate the area of a circle. Its as easy as pi.
Page 8: How to calculate the area of a circle. Its as easy as pi.

The length of this line

segment is the

circumference

of the

circle.314 cm

Page 9: How to calculate the area of a circle. Its as easy as pi.

The circumference is the same length as 3 diameters plus .14

of another diameter.

Page 10: How to calculate the area of a circle. Its as easy as pi.

So, circumference = diameter x 3.14

Page 11: How to calculate the area of a circle. Its as easy as pi.
Page 12: How to calculate the area of a circle. Its as easy as pi.
Page 13: How to calculate the area of a circle. Its as easy as pi.
Page 14: How to calculate the area of a circle. Its as easy as pi.
Page 15: How to calculate the area of a circle. Its as easy as pi.

Does this look familiar?

Page 16: How to calculate the area of a circle. Its as easy as pi.

O.K., now it’s time to move forward with some

new stuff.

Page 17: How to calculate the area of a circle. Its as easy as pi.

How in the world would you find the area of a circle?

Page 18: How to calculate the area of a circle. Its as easy as pi.

Remember, area is always measured in square units.

Page 19: How to calculate the area of a circle. Its as easy as pi.

Remember that the area of a rectangle is length x width because you’re calculating the total number of squares inside of the rectangle.

2

4

Page 20: How to calculate the area of a circle. Its as easy as pi.

That’s fine and dandy, but a circle is not a polygon. It does not have

straight sides; it has curves.

Page 21: How to calculate the area of a circle. Its as easy as pi.

How are we going to get around these curves?

Page 22: How to calculate the area of a circle. Its as easy as pi.

Imagine chopping up the circle as if it were a pizza.

Page 23: How to calculate the area of a circle. Its as easy as pi.

Now, let’s rearrange our “pizza” into another shape.

Page 24: How to calculate the area of a circle. Its as easy as pi.
Page 25: How to calculate the area of a circle. Its as easy as pi.
Page 26: How to calculate the area of a circle. Its as easy as pi.
Page 27: How to calculate the area of a circle. Its as easy as pi.
Page 28: How to calculate the area of a circle. Its as easy as pi.
Page 29: How to calculate the area of a circle. Its as easy as pi.
Page 30: How to calculate the area of a circle. Its as easy as pi.
Page 31: How to calculate the area of a circle. Its as easy as pi.

PRESTO!

Page 32: How to calculate the area of a circle. Its as easy as pi.

Great Mr. Dunlap! But what in the world is this?

Page 33: How to calculate the area of a circle. Its as easy as pi.

Believe it or not, this is really our “friend” the parallelogram.

And, we know how to calculate the area of a

parallelogram.

Page 34: How to calculate the area of a circle. Its as easy as pi.

Rats! He always has an answer for everything.

Page 35: How to calculate the area of a circle. Its as easy as pi.

Area = Base x Height

Base

Height

Page 36: How to calculate the area of a circle. Its as easy as pi.

To find the area of the circle (which is now a parallelogram), we just need to multiply the Base by the

Height.

Base

Height

Page 37: How to calculate the area of a circle. Its as easy as pi.

Base

Radius

Wait a minute! The height of this “parallelogram” is really the radius

of the circle.

Page 38: How to calculate the area of a circle. Its as easy as pi.

1/2 of Circumference

Radius

Wait a minute! The Base is really 1/2 of the circumference.

Page 39: How to calculate the area of a circle. Its as easy as pi.

1/2 of Diameter x

Radius

Wait a minute! The circumference is

really Diameter x

Page 40: How to calculate the area of a circle. Its as easy as pi.

Radius x

Radius

Wait a minute! 1/2 of a Diameter is really a Radius.

Page 41: How to calculate the area of a circle. Its as easy as pi.

Base

Height

So if we multiply the Base x Height

Page 42: How to calculate the area of a circle. Its as easy as pi.

We are really multiplying

Radius x Radius x

Radius x

Radius

Page 43: How to calculate the area of a circle. Its as easy as pi.

Practice Time!

Page 44: How to calculate the area of a circle. Its as easy as pi.

1) Now let’s try this formula. Find the area of this circle.

5 cm

Page 45: How to calculate the area of a circle. Its as easy as pi.

5 x 5 x 3.14 = 78.5 square cm

5 cm

Page 46: How to calculate the area of a circle. Its as easy as pi.

2) Find the area of this circle.

6 cm

Page 47: How to calculate the area of a circle. Its as easy as pi.

6 x 6 x 3.14 = 113.04 square cm

6 cm

Page 48: How to calculate the area of a circle. Its as easy as pi.

3) Find the area of this circle.

9 cm

Page 49: How to calculate the area of a circle. Its as easy as pi.

9 x 9 x 3.14 = 254.34 square cm

9 cm

Page 50: How to calculate the area of a circle. Its as easy as pi.

4) Find the area of this circle.

20 cm

Page 51: How to calculate the area of a circle. Its as easy as pi.

10 x 10 x 3.14 = 314 cm2

20 cm

Make sure that you use the radius of

the circle.

Page 52: How to calculate the area of a circle. Its as easy as pi.

5) Find the area of this circle.

14 cm

Page 53: How to calculate the area of a circle. Its as easy as pi.

7 x 7 x 3.14 = 153.86 cm2

14 cm

Make sure that you use the radius of

the circle.

Page 54: How to calculate the area of a circle. Its as easy as pi.

6) Find the area of this circle.

22 cm

Page 55: How to calculate the area of a circle. Its as easy as pi.

11 x 11 x 3.14 = 379.94 cm2

22 cm

Page 56: How to calculate the area of a circle. Its as easy as pi.

Area = Radius x Radius x

It’s as easy as pi.