Starter• Calculate the Circumference of each of these shapes. Remember

that in any circle:Circumference = π x Diameter

orC = πd

orC = 2πr

a) b) c)

10cm 8cm4cm

Area of a Circle

• We have looked at the Area of various shapes over the last few lessons

• We have also looked at finding the area of ‘compound shapes’

• Today we are going to be focusing on circles

• We will be learning a new formula

Area of a Circle

Learning ObjectivesAll will be able to use the formula to work out the Area

of circles (Level 6)

Most will be able to calculate the areas of semi-circles and quarter-circles (Level 6/7)

Some will be able to apply these formulae to practical questions (Level 6/7)

Demonstration of the Area of a Circle formula

Area of a Circle

• Area of a Circle

The area of a circle is given by the following formula…

A = πr2

A = Areaπ = ‘pi’ = 3.14…… (on calculator)r = radius of the circle

Area (A)

Radius (r)

Area of a Circle

• Example Question

a) A circle has a radius of 6cm. Calculate its Area.

6cmArea

A = πr2

A = π x 62

A = 113.10cm2 (2dp)

Area of a Circle

• Example Question

b) A circle has a diameter of 9cm. Calculate its Area.

9cm

Area

A = πr2

A = π x 4.52

A = 63.62cm2 (2dp)

Area of a Circle

• Example Question

c) Calculate the Area of this semicircle…

8m

Area

A = πr2

A = π x 82

A = 201.06m2 (2dp)

Then divide by 2

201.06 ÷ 2 = 100.53m2

16m

Area of a Circle

• Example Question

d) How would you work out the area of this shape, made from a square and 4 semi-circles?

8cm

8cm

8cm8

cm

The Square

8 x 8= 64 cm2

The 4 semi-circles

You can imagine opposite sides could be pushed together to make a full circle

A = πr2

A = π x 42

A = 50.27 cm2

A = 100.53 cm2

Total 64 + 100.53 = 164.53 cm2

Radius = 4

Double (2 circles in total)

Summary

• We have learnt another formula involving circles

• We have looked at working out the Area of a Circle

• We have seen a variety of different problems on this topic