# Area of Circles

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Category: Education

## Presentation Description

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By: deasabathulachak (63 month(s) ago)

very good

## Presentation Transcript

### How to calculate the area of a circle.:

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

### Let’s first make sure that we understand the difference between circumference and area.:

Let’s first make sure that we understand the difference between circumference and area.

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

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

### Imagine that the circle is straightening itself out.:

Imagine that the circle is straightening itself out.

### PowerPoint Presentation:

The length of this line segment is the circumference of the circle. 314 cm

### The circumference is the same length as 3 diameters plus .14 of another diameter.:

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

### So, circumference = diameter x 3.14:

So, circumference = diameter x 3.14

### Does this look familiar?:

Does this look familiar?

### O.K., now it’s time to move forward with some new stuff.:

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

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

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

### Remember, area is always measured in square units.:

Remember, area is always measured in square units.

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

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

### That’s fine and dandy, but a circle is not a polygon. It does not have straight sides; it has curves.:

That’s fine and dandy, but a circle is not a polygon. It does not have straight sides; it has curves.

### How are we going to get around these curves?:

How are we going to get around these curves?

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

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

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

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

PRESTO!

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

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

### Believe it or not, this is really our “friend” the parallelogram. And, we know how to calculate the area of a parallelogram.:

Believe it or not, this is really our “friend” the parallelogram. And, we know how to calculate the area of a parallelogram.

### Rats! He always has an answer for everything.:

Rats! He always has an answer for everything.

### Area = Base x Height:

Area = Base x Height Base Height

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

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

### Wait a minute! The height of this “parallelogram” is really the radius of the circle.:

Base Radius Wait a minute! The height of this “parallelogram” is really the radius of the circle.

### PowerPoint Presentation:

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

### PowerPoint Presentation:

1/2 of Diameter x  Radius Wait a minute! The circumference is really Diameter x 

### PowerPoint Presentation:

Base Height So if we multiply the Base x Height

Practice Time!

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

1) Now let’s try this formula. Find the area of this circle. 5 cm

### 5 x 5 x 3.14 = 78.5 square cm:

5 x 5 x 3.14 = 78.5 square cm 5 cm

### 2) Find the area of this circle.:

2) Find the area of this circle. 6 cm

### 6 x 6 x 3.14 = 113.04 square cm:

6 x 6 x 3.14 = 113.04 square cm 6 cm

### 3) Find the area of this circle.:

3) Find the area of this circle. 9 cm

### 9 x 9 x 3.14 = 254.34 square cm:

9 x 9 x 3.14 = 254.34 square cm 9 cm

### PowerPoint Presentation:

4) Find the area of this circle. 20 cm

### PowerPoint Presentation:

10 x 10 x 3.14 = 314 cm 2 20 cm Make sure that you use the radius of the circle.

### PowerPoint Presentation:

5) Find the area of this circle. 14 cm

### PowerPoint Presentation:

7 x 7 x 3.14 = 153.86 cm 2 14 cm Make sure that you use the radius of the circle.

### PowerPoint Presentation:

6) Find the area of this circle. 22 cm

### PowerPoint Presentation:

11 x 11 x 3.14 = 379.94 cm 2 22 cm

### PowerPoint Presentation:

Area = Radius x Radius x  It’s as easy as pi.