1. Warm-Up’s

2. Warm-Up’s 2.

3. Warm-Up’s

4. The circumference and Area of a circle

5. What is the formula relating the circumference to the diameter?
centre
Diameter
Radius

6. This means APPROXIMATELY EQUAL TO
C = ? x d
People knew that the circumference is about 3 times the diameter but they wanted to find out exactly.
C ≈ 3 x d
This means APPROXIMATELY EQUAL TO

7. The exact true value is……………
UNKNOWN!!

8. An approximation to π
π≈ forever….

9. What about the AREA of a circle?
First consider a square
The area of this square
in terms of r is
A= 2r x2r = 4r2 r 2r

10. What about the AREA of a circle?
Now consider a circle inside the square
The area of the circle must be less than the are of the square
A < 4r2 2r r 2r
Area = ? xr2

11. Finding a formula for the area of a circle

12. C= πd or C=2πr
Semi-circle=πr πr r

13. Area of Rectangle= Base x Height
Area = πr x r
Area =πr2

14. The Area and Perimeter of a Circle
A circle is defined by its diameter or radius
radius
The perimeter or circumference of a circle is the distance around the outside
The area of a circle is the space inside it
Diameter
The ratio of π (pi)
π is an irrational number whose value to 15 decimal places is
π = We usually say π≈3.14
The circumference is found using the formula
C=π d or C= 2πr (since d=2r)
The area is found using the formula
A=πr2

15. The Area and Perimeter of a Circle
A circle is defined by its diameter or radius
radius
The perimeter or circumference of a circle is the distance around the outside
The area of a circle is the space inside it
Diameter
The ratio of π (pi)
π is an irrational number whose value to 15 decimal places is
π = We usually say π≈3.14
The circumference is found using the formula
C=π d or C= 2πr (since d=2r)
The area is found using the formula
C=πr2

16. Videos on Circles A Rap about circles