Starter Calculate the Circumference of each of these

Starter • Calculate the Circumference of each of these shapes. Remember that in any circle: Circumference = π x Diameter or C = πd or C = 2πr a) b) 10 cm c) 8 cm 4 cm

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 Objectives All 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 = πr 2 A = Area π = ‘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 6 cm. Calculate its Area. 6 cm Area A = πr 2 A = π x 62 A = 113. 10 cm 2 (2 dp)

Area of a Circle • Example Question b) A circle has a diameter of 9 cm. Calculate its Area 9 cm A = πr 2 A = π x 4. 52 A = 63. 62 cm 2 (2 dp)

Area of a Circle • Example Question c) Calculate the Area of this semicircle… Area A = πr 2 A = π x 82 16 m 8 m A = 201. 06 m 2 (2 dp) Then divide by 2 201. 06 ÷ 2 = 100. 53 m 2

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? The Square 8 x 8 = 64 cm 2 8 cm The 4 semi-circles 8 cm You can imagine opposite sides could be pushed together to make a full circle A = πr 2 Radius = 4 A = π x 42 8 cm A = 50. 27 cm 2 A = 100. 53 cm 2 Double (2 circles in total) Total 64 + 100. 53 = 164. 53 cm 2

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