The CircleThe Circle

The language of circlesThe language of circles

• Circumference: The distance round Circumference: The distance round the circlethe circle

• Diameter: the distance from one Diameter: the distance from one point on the circumference to point on the circumference to another point passing through the another point passing through the centrecentre

• Radius: the distance from the centre Radius: the distance from the centre to the circumferenceto the circumference

Formulae of circlesFormulae of circles

• AreaArea: : A = A = ππrr22

• Circumference:Circumference: C = C = ππDD

ππ= 3.14 OR = 3.14 OR ππ on your calculator on your calculator

You must learn these facts!!! You must learn these facts!!!

Calculating the Calculating the circumferencecircumference

12 cm15 cm

C = πd πd

C = C = ππ x 12 = 37.68 cm x 12 = 37.68 cm

C= ππdd

C = C = ππ x 15 = 47.1 cm x 15 = 47.1 cm

Calculating CircumferencesCalculating Circumferences

4cm

Radius = 4 cm so diameter = 2 x 4 = 8 cm

C = πd

C= π x 8 = 25.04 cm

REMEMBER: The radius is half of the diameter

Calculating areasCalculating areas

12 cm

20 cm

D = 12 cm D = 20 cm

R = 6 cm r = 10 cm

A = πr2 A = πr2

A = π x 6 x 6 = 113.1 cm2 A = π x 10 x 10 = 314 cm2