1. Area of Circles and Parts of Circles

2. Finding the area of a circle
The area of a circle is found using the formula
A = r2

3. Practice Finding the area of a circle
A =  cm2
or cm2

4. Practice Finding the area of a circle
A = 6.734 cm2
or cm2

5. Practice Finding the area of a circle
Find the area of the shaded region
A = 36 - 9 = 27 u2
or u2 3 6

6. Practice Finding the area of a circle
Find the area of the circle if the area of the square = 144 m2
The circle has a diameter of 12 m so A = 36 m2 or m2

7. Practice Finding the area of a circle
Find the area of the shaded region if the side of the square = 10 cm
The area is 100 cm2 - 25 cm2 or cm2

8. Practice Finding the area of a circle
Find the area of the shaded region if the side of the square is 12 cm.
The area is 144 cm2 - 4(9) cm2 or 30.9 cm2

9. Finding the radius when area is known
Since the formula for the area of a circle is A = πr2, the radius can be determined if the area is known.
If A = 49π, then r2 = 49. If r2 = 49, then r = 7.

10. Finding the radius when area is known
Find the radius for each circle
A = 144π
A = 36π
A = 81π
A = 25π
5. A = 100π
r = 12
r = 6
r = 9
r = 5
r = 10

11. Finding the circumference when area is known
To find the circumference when the area is known, first find the radius and then use it to find the circumference.
A = 49π so r = 7 and d = 14
C = 14π

12. Finding the circumference when area is known
Find the circumference for each circle
A = 144π
A = 36π
A = 81π
A = 25π
5. A = 100π
C = 24π
C = 12π
C = 18π
C = 10π
C = 20π

13. THE END