More about algebra KN4 - Amazon Web Services · Back Next The ‘d’ stands for diameter. The...

More about AlgebraLearning Objective: To use formulae to find the area and the circumference of a circle.

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This is the formula to find the circumference of a circle.

What does the ‘d’ stand for? What does the π mean?

c=πd


The ‘d’ stands for diameter. The symbol π is called pi. Pi is a number that has trillions

of digits! Pi can be shortened to 3.14.

c=πddiameter


What is the circumference of this circle?

The diameter is 5cm.

c=πd5cm


Did you remember to use

3.14 as your value of π?

c=πd

5cm 15.7cm c=3.14 x 5

c=15.7cm


What is the circumference of this circle?


c=πd18cm


Did you know most calculators have a button for

π?

c=πd

18cm

56.5cm c=3.14 x 18c=56.5cm


What to you think this formula is for?

What does the ‘a’ stand for? What does the ‘r’ stand for?

a=πr2


The ‘a’ stands for area. The ‘r’ stands for radius. The

radius is half of the diameter of a circle. This formula will

find the area of a circle.diameter

a=πr2

radius


What is the area of this circle?

The radius is 8cm.

8cm

a=πr2


Did you get the correct area?

201cm2 a=3.14 x 82a=πr2

8cm a=3.14 x 64a=201cm2


What is the area of this circle?


24cm

a=πr2

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Did you get the correct area?

452.2cm2 a=3.14 x 122a=πr2

a=3.14 x 144a=452.2cm2

24cm 12cm

This formula is for the circumference of a circle.

Can you find the perimeter of this semicircle?


Plenary c=πd15cm


p=½πd + dTo find the perimeter of the

semicircle you need to work out the circumference of the circle, divide it

by two and add the diameter.

diameter


Did you get the correct

perimeter?p=½ (3.14 x 15) +15p=½ (47.1) +15

p=38.55cm

p=½πd + d

p=23.55 + 15

38.55cm

This formula is for the area of a circle. Can you find the

area of this semicircle?


15cm

a=πr2


a=½πr2To find the area of the semicircle you

need to work out the area of the circle and divide it by two.

diameter

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Did you get the correct area?a=½ (3.14 x 7.52)

a=½ (3.14 x 56.25)

a=88.3cm2

a=½πr2

a=½ (176.6)88.3cm2

15cm 7.5cm

More about algebra KN4 - Amazon Web Services · Back Next The ‘d’ stands for diameter. The...

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