1. 1.5 Measurement
AS 91030

2. Area of Circles I can find the area of a circle
Learning objectives
20 May 2019
I can find the area of a circle
I can find the area of part of a circle
I can find the area of an annulus
I can find the radius when I know the area

3. Area of Circles The rule you need to use is
Area = Πr² (Π x radius x radius)
when the radius = 12 cm
Area = Π x 12² (Π x 12 x 12)
= 452cm²

4. Parts of circles The rule you need to use is
Area = Πr² (Π x radius x radius)
but now we only have half a circle!
Area = Πr²÷ 2
when the radius = 4m
Area = Πx4²÷ 2
= 25 m²

5. The rule you need to use is
Area = Πr² (Π x radius x radius)
but now we only have part of a circle!
Area = 3 4 Πr²
when the radius = 6m
Area = 3 4 πx6² = 84.8 m²

6. The rule you need to use is
Area = Πr² (Π x radius x radius)
but now we only have part of a circle!
Area = Πr²
when the diameter = 8m
Area = πx4² = 27.9 m²
200°

7. Annulus area = 𝜋 x 8² - 𝜋 x 3² = 173 cm² Think donuts! 8 cm
To find the area of the pink section
Find the area of the big circle
Find the area of the small circle
do a subtraction
3cm
area = 𝜋 x 8² - 𝜋 x 3² = 173 cm²

8. I can find the radius when I know the area
The rule you need to use is
Area = Πr² (Π x radius x radius)
when the area = 150 cm²
150 = 𝜋𝑟²
𝑟² = 150 𝜋
r =
150 𝜋
r = 6.9 cm

9. Success Criteria I can find the area of a circle
I can find the area of part of a circle
I can find the area of an annulus
I can find the radius when I know the area