Special words The Circle Finding the circumference Finding

Special words The Circle Finding the circumference Finding the area

Special Words The distance from the centre edge all theone way of a circle around theto the another edge circle (its is called (passing the is perimeter) Radius through the called the centre) is Circumference called the Diameter

Objective Be able to find the circumference of a circle. Be able to find the perimeter of shapes with circular parts.

Finding the circumference The formula for the circumference is Sometimes we are given the diameter C = πd 8 cm C = 3. 14 x 8 π = 3. 14 (2 dp) = 25. 12 cm

Finding the circumference C = πd 14 cm C = 3. 14 x 14 = 43. 96 cm π = 3. 14 (2 dp)

Finding the circumference Sometimes we are given the radius, r But this is just half of the diameter, so we use 2 r instead of d π = 3. 14 (2 dp) Now the formula for the circumference is C = 2πr 5 cm C = 2 x 3. 14 x 5 = 31. 4 cm

Finding the circumference C = 2πr 3 m C = 2 x 3. 14 x 3 = 20. 09 m π = 3. 14 (2 dp)

What is the perimeter? 3 m 12 m The perimeter is the distance around the outside of the shape

What is the shape made of? 3 m 12 m

What is the shape made of?

So really we have two shapes: A rectangle and a circle So this part gives us 12 m + 12 m = 24 m 12 m = 2πr For this part, we find the Ccircumference C = 2 x 3. 14 x 3 So the total perimeter is 24 m + 18. 84 m = 42. 84 m = 18. 84 m 3 m

Objective Be able to find the area of a circle. Be able to find the area of compound shapes with circular parts

Finding the area Usually we are given the radius, r 7 cm π = 3. 14 (2 dp) The formula for the area of a circle is A = π r 2 A = 3. 14 x 72 = 3. 14 x 7 =153. 86 2 cm

Finding the area If you are given the diameter, simply half this to find the radius first. Here r = 4 m 8 m π = 3. 14 (2 dp) The formula for the area of a circle is A = π r 2 A = 3. 14 x 42 = 3. 14 x 4 = 50. 24 2 m