- Slides: 24
diameter is 4 cm!
radius is 9 cm!
diameter is 10 cm! semi + semi = whole circumference!
diameter is 5 cm! semi x 4 = 2 circumferences!
Area of a Circle Area : The space inside a shape!
Recall. . • EVERY line from the centre of the circle to the circumference is a radius.
L. O. To be able to discover the formula to find the Area of a Circle • Take a circle sheet each please! • Prepare: – a pair of scissors – 2 colours
Step 1: Colour Half and Half Step 2: Cut the outline of the Circle
Step 3: Cut out each sector
Step 4: Re-arrange the pieces Alternate colours Alternate directions
Okay…what does this shape look like?
Yes, a Parallelogram!
How do we find the Area of a Parallelogram? Area = Base x Height
What’s our Base in this case? (outline of pink part) Base = ½ Circumference
What’s the Height? Height = radius of circle
How do we find the Circumference of a Circle? Circumference = 2 x π x radius =2πr
Therefore…to find the Area of a Circle • Area of Circle = Area of Parallelogram = Base x Height = ½ x circumference x radius = ½x 2πrxr = πr²
Area of Circle = π r ²
Example 1 4 m What is the area of this circle? A= r² A= x 4 x 4 A = 50. 3 m² (1 d. p. ) Press Then x 4 =
Example 2 ? 7 cm 14 cm What is the area of this circle? A= r² r = ½ x 14 = 7 cm A= Don’t forget! x 7 x 7 A = 153. 9 cm² (1 d. p. ) Press Then x 7 =