Area of Circles

Area of a Circle

​This lesson will follow the notes provided.
Please watch the videos, answer the questions, AND fill out the notes! Remember - the notes will be a part of the Unit 3 Notebook check!!

Watch the video. The captions are helpful!

Area of a Circle

Multiple Choice

The radius is from the center of a circle to one edge.

• True

• False

​Circle 1

Next we need to find out what the radius is. This one is labeled r = 3 in.


We can also count the number of squares that are shaded from one edge to the center.

​

​Circle 1

​Circle 1

​The () around the 3 squared are to show the 2 only works on that number. You do not square pi

​Circle 1

Type

​Circle 1

​Circle 1

Sometimes you are not given boxes to count or a radius.

This question gives you a diameter.

When this happens divide the diameter by 2 to get the radius then continue like normal!

​Circle 2

​Circle 2

Multiple Choice

10 ÷ 2 =

• 12

• 8

• 20

• 5

​Circle 2

​Circle 2

Multiple Choice

$$5\times5=$$

• 10

• 0

• 25

• 1

​Circle 2

​Circle 2

​Yes I know the calculator says 78.53981634, not 78.54 but it is ok to round your answer to a smaller number..
In this question I rounded to the hundredths place, the number after 3 is 9, since 9 is bigger than 5 we round the 3 up to 4.

Multiple Choice

Round the number to the hundredths place

27.36475684

• 20

• 27.36

• 27.4

• 27.36475684

Try this one on your own while I walk you through it.

Do you have a radius or a diameter?

​

Circle 3

Fill in the Blanks

Write the formula for finding the area of a circle.

Next, replace what you know.


Hint you should know the radius.

​

Circle 3

Drag and Drop

​

Placeholder

​ = ​

Placeholder

​​

Placeholder

Drag these tiles and drop them in the correct blank above

A

6

C

12

Now simplify the exponent to write the area in terms of pi

Circle 3

Multiple Choice

What is the area in terms of $$\pi$$ ?

• $$A=12\pi$$

• $$A=0\pi$$

• $$A=36\pi$$

• $$A=1\pi$$

Finally, multiply to find the area.

Circle 3

Math Response

What is the area of the circle?

Type answer here

Correct Answer: 113.04m^2

Deg^°

Rad

These next few questions are for practice, they are not in your notes. You can write them on the next page or in the margins if you would like extra examples.

Dropdown

The radius is ​

Select answer

.

When I plug in what I know I have A = ​

Select answer

​

Select answer

.

In terms of π the area is ​

Select answer

.

The area of the circle is​

Select answer

Fill in the Blanks

Multiple Choice

To find the radius I...

• Add 2

• Subtract 2

• Multiply by 2

• Divide by 2

Math Response

What is the area of the circle?

Type answer here

Correct Answer: 12.57

Deg^°

Rad

What happens when you know the area but not the radius?!

Look at the second notes sheet, #1.

A circle has an area of 78.5 square inches. What is the radius?

A circle has an area of 78.5 square inches. What is the radius?

A circle has an area of 78.5 square inches. What is the radius?

A circle has an area of 78.5 square inches. What is the radius?

​To find a square root on the calculator click this then type in the number.

Multiple Choice

What number, multiplied by itself, will equal 25?

• 7

• 5

• 4

• 6

#2

A circular sprinkler system is installed and waters an area of 28.29 square yards.
What is the radius of the circle?

#2

A circular sprinkler system is installed and waters an area of 28.29 square yards.
What is the radius of the circle?

#2

A circular sprinkler system is installed and waters an area of 28.29 square yards.
What is the radius of the circle?

Multiple Choice

What number, when multiplied by itself is 9?

• 1

• 2

• 3

• 4

#2

A circular sprinkler system is installed and waters an area of 28.29 square yards.
What is the radius of the circle?

Drag and Drop

#3. Jada says that if you are given the circumference of a circle, you have enough information to find the area of the circle. Is Jada correct?



Jada is ​

Placeholder

. To find the area, you need the ​

Placeholder

. If you have the circumference, you can work​

Placeholder

to determine the ​

Placeholder

Drag these tiles and drop them in the correct blank above

correct

radius

backwards

forwards

incorrect

diameter

This describes the perimeter of the circle, it is the line making the circle.

Circumference

This describes everything inside the circumference of the circle.

​​Area

Dropdown

#4.

The amount of fencing around a circular garden. ​

Select answer

The amount of frosting needed to cover a cookie. ​

Select answer

The amount of crust needed to cover a pie. ​

Select answer

The distance traveled in one lap around a circular track. ​ ​

Select answer

5.

Two different trees are being planted in an outdoor garden. Each tree requires a specific amount of space for the roots to grow.
How much more space will tree II (two) require?

​Start with what you know about both trees...

​Tree II has a radius of 9 ft.

5.

Two different trees are being planted in an outdoor garden. Each tree requires a specific amount of space for the roots to grow.
How much more space will tree II (two) require?

​What do you need to know?

​How many more square feet will tree II need?
In other words
Area of tree II - Area of tree I

5.

Two different trees are being planted in an outdoor garden. Each tree requires a specific amount of space for the roots to grow.
How much more space will tree II (two) require?

​Find the areas (plan and work)

5.

Two different trees are being planted in an outdoor garden. Each tree requires a specific amount of space for the roots to grow.
How much more space will tree II (two) require?

Solution (answer the question)
Area of Tree II - Area of Tree I = ?
254.47 - 201.06 = 53.41

Poll

On a scale of 1 - 5 how well do you understand how to find area of a circle?

(No wrong answers!)

• 1 - not at all and I read everything on here!

• 2 - a little bit

• 3 - meh kind of

• 4 - I have a question but I think I got it

• 5 - I totally got it!