1. Discovering Area of a Circle
Student materials: Copy of circle picture, study guide ws., scissors & glue sticks.
Discovering
Area of a
Circle

2. Area of a Circle 10.4 Notes Area = (pi)(radius)2 Area = r2 Example
Copy the equation (don’t just solve in your head)
Substitute the numbers for the variables
Solve
Example

3. I can… Determine the area of circles Self Assessment
5- I can do it without help & teach others.
4- I can do this with no help, but I don’t know if I can explain it.
3- I can do this with a little help.
2- I can do this with a lot of help!
1- I don’t have a clue.

4. Area of a Circle Discovery
For Learning to Happen:
Pay close attention to this lesson.
Listen to my instructions to discover the area of a circle formula.
Do NOT work ahead!!!!

5. On your White Sheet of Paper
Area of a Circle Discovery
On your White Sheet of Paper
Label the circumference, diameter and radius on your circle.
Diameter
Radius
Circumference

6. Area of a Circle Discovery
Carefully cut out the circle on the bolded lines. Cut along the diameter to cut the circle in half. You should have 2 halves.

7. Area of a Circle Discovery
Start from the diameter and cut the 4 pieces. DO NOT CUT IT TO THE EDGE! Open the semicircles and bend them out so they look like 4 connected triangles.

8. Area of a Circle Discovery
Fit the 4 triangles together so that as one is facing up, the other is facing down. Glue these pieces together on your study guide handout. Make sure your words on facing up!
radius
Circumference

9. Area of a Circle Discovery
Answer the following questions on your
Study Guide worksheet.
What does your new figure look like?
Parallelogram
2a. Draw your answer here. Label base & height
2b. How do you find the area of a parallelogram?
Base x Height
height
base

10. Area of a Circle Discovery
3. Draw your area of a circle figure below. In knowing that you need to find the base and height of your new figure to calculate the area, what is the height of your new figure? Label your picture. 4. What is the bottom base of your new figure? Label your picture above. Hint: Half of the circumference.
Height = radius
pi x radius

11. Area of a Circle Discovery
If you know the base and height of your new figure can you find the area? Take your base and multiply it by your height. Show your work!
6. Simplify your formula.
7. Write out how you find the area of a circle.
Pi times radius squared.

12. Here is what we just did:
Recap Video
Here is what we just did:
Area of a Circle

13. How do I remember the formula?
Do you like pie?
C = d
Cherry Pies Delicious
A = r2
Apple Pies Are Too

14. Let’s Practice
Take out a calculator to try to solve the following problems on area of a circle.

15. Practice with the teacher
6 in.
Find the area of the circle.
= 3.14

16. Find the area of the circle.
Your Turn
Find the area of the circle.
11 m.
= 3.14

17. What is the radius if the diameter is 10 ft?
Your Turn
Find the area of the circle.
10 ft.
= 3.14
What is the radius if the diameter is 10 ft?

18. What is the radius if the diameter is 10 ft?
Your Turn
Find the area of the circle.
4 ft.
= 3.14
What is the radius if the diameter is 10 ft?

19. What is the radius if the diameter is 10 ft?
Your Turn
Find the area of the circle.
20 cm.
= 3.14
What is the radius if the diameter is 10 ft?

20. I can… Determine the area of circles Self Assessment
5- I can do it without help & teach others.
4- I can do this with no help, but I don’t know if I can explain it.
3- I can do this with a little help.
2- I can do this with a lot of help!
1- I don’t have a clue.

21. Area of a Circle 10.4 Notes Area = (pi)(radius)2 Area = r2
Copy the equation (don’t just solve in your head)
Substitute the numbers for the variables
Solve