LO:Tocalculatethecircumferenceandarea

ofacircle

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TounderstandthedifferentpartsofacircleTouseaformulatocalculateananswer

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Drawacirclewitharadiusof1.

Thedistancehalfwayaroundtheedgeofthe

circlewillbe3.14159265...anumberknownasPi

Pi (π)

Oryoucoulddrawacirclewithadiameterof1.

Thenthecircumference(thedistancealltheway

aroundtheedgeofthecircle)willbePi

Pi (the symbol is the Greek letter π) is: The ratio of the Circumference to the Diameter of a Circle.

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Pi (π)

Finding Pi Yourself

Measure around the edge (the circumference): 82cm

Measure across the circle (the diameter): 26cm

Divide: 82 cm / 26 cm = 3.1538... That is pretty close to π. Maybe if I measured more accurately?

For our calculations we will use pi as 3.14

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Finding the circumference of a circle (the perimeter)

Find the circumference of a circle, given the diameter:

Example1

4cm diameter

Circumference=π×diameter

Circumference = π × 4 = 12·6cm (1 d.p.)

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Finding the circumference of a circle (the perimeter)

Find the circumference of a circle, given the radius:

Example2

2cm radius

Circumference=π×diameter=π×radiusx2

Circumference = π × (2 x 2) = π × 4 = 12.6cm (1 d.p.)

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Finding the circumference of a circle (the perimeter) Circumference=π×diameter=π×radiusx2

3cm

diameter

6cm

diameter

1.5cm

radius 3.5cm

radius

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Finding the area of a circle (the perimeter)

4cm radius

Area=π×radius2

Area = π × 42

= π × 16 = 50·2 cm2 (1 d.p.)

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Finding the area of a circle (the perimeter)

5cm

radius

Area=π×radius2

4.5cm

radius

12cm

radius

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Success Criteria: Identify the diameter and radius Choose the correct formula Remember pi = 3.14 Round your answer to 1dp Check your answer

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EXTENSION

3.1 cm

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EXTENSION

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Plenary

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Plenary

Whichdealisbettervalueformoney?

12 inch pizza

£7.99!!!

2 x 8 inch pizzas

£7.99!!!

Whichdealisbettervalueformoney?

12 inch pizza£7.99!!!

2 x 8 inch pizzas£7.99!!

!

Deal1AreaofPizza=π×radius2

=π×62 =π×36 =113inch2

Deal2AreaofPizza=π×radius2

=π×42 =π×16 =50.24inch2

2Pizzas =50.24x2 =100.5inch2