CIRCLES 2 radius circumference centre tangent diameter chord

CIRCLES 2

radius circumference centre tangent diameter chord

area of circle Area of red square ‹ A ‹ 4 r 2

Area of blue square 2 r 2 area of circle ‹ ‹ A

Let’s look at the area inside a circle

Let’s use a diagram to help 6 r ‹ c ‹ 8 r Explain why the statement must be true

A group of students measured the radius & estimated the area of five circles to see how they were related. Here are their results

Here is their graph The equation of the curve is A = 3. 1 r 2

C= πd C = 2π r A = π r 2 π x 2 x π x d π x r r x r

This circle has a diameter of 20 cm Find the radius, circumference & area of the circle Use π = 3. 14

Radius = 20 cm d 2 = 20 2 = 10 cm circumference = = πd π x 20 = 3. 14 x 20 = 62. 8 cm area = π r 2 = 3. 14 x 10 = 314 cm 2

Choose a problem semicircle sector End

Calculate the perimeter and area of this semicircle Use π = 3. 14 12 m

Calculate the perimeter and area of this semicircle Use π = 3. 14 12 m Perimeter = πd + d 2 2 πr Area = 2 = (3. 14 x 12) + 24 = 3. 14 x 12 x 6 = 37. 68 + 24 = 3. 14 x 12 x 6 = 61. 68 m = 226. 08 m 2

Calculate the perimeter and area of this sector 8 cm 60 o Use π = 3. 14

Calculate the perimeter and area of this sector 8 cm 60 o Perimeter = πd + 2 r 6 = (3. 14 x 16) + 16 6 = 24. 4 cm Use π = 3. 14 2 πr Area = 6 = 3. 14 x 8 6 = 34. 5 cm 2

End