2. Calculating The Area Of a Circle So far In this topic we have come up with a formula to calculate the circumference of a circle : C = πD Now we need a formula to calculate the area of a circle!

3. The Formula! Area of a circle = π x radius 2 OR, in short, A = π r 2 r

4. Examples : 1.Calculate the areas of the following circles : (a) 4cm (b) 17.5cm A = π r 2 A = π x 4 2 A = π x 16 A = 50.27 (to 2d.p.) A = π r 2 A = π x 8.75 2 A = π x 76.5625 A = 240.53 (to 2d.p.)

5. A slightly more difficult example! 2. The brim of Professor McGonagalls witch’s hat is made by cutting a small circle out of the middle of a larger circle. (a)Calculate the area of the larger circle (b)Calculate the area of the smaller circle (c)By subtracting, calculate the area of the brim 15cm 7cm

6. Area of Large Circle :A = π r 2 A= π x 15 2 A = π x 225 A = 706.86 (to 2d.p.) Area of Inner Circle :A = π r 2 A = π x 7 2 A = π x 49 A = 153.94 Area Of Brim =Area of Large Circle – Area of Inner Circle = 706.86 – 153.94 = 552.92 cm 2 15cm 7cm

7. 24cm Find the shaded area. Square A=24  24 = 576cm² 1 circle A=  r² r =6cm =   6  6 A= 113.097 … Area of 4 circles = 113.097  4 = 452.388 = 452cm² Shaded area = 576cm² - 452cm² = 124cm²

8. MIXED QUESTIONS 4cm 10cm Find the perimeter and the area of this shape. Perimeter Area C =  d =   10 Perimeter = 31.4 + 4 + 4 = 39.4cm A=  r² =   5  5 = 78.5cm² CircleRectangle A= 4  10 = 31.4cm = 40cm² Total area = 78.5 + 40 = 118.5cm²

9. 60cm 40cm Find the shaded area. Shaded area area of rectangle – area of semi-circle A = 60  40 = 2400cm² A=  r²  2 =   30  30  2 r =30cm = 1413.7… = 1414cm² Shaded area = 2400 - 1414 = 986cm²