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Warm-Up’s. 2. Warm-Up’s The circumference and Area of a circle.

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Presentation on theme: "Warm-Up’s. 2. Warm-Up’s The circumference and Area of a circle."— Presentation transcript:

1 Warm-Up’s

2 2.

3 Warm-Up’s

4 The circumference and Area of a circle

5 Diameter Radius centre What is the formula relating the circumferenc e to the diameter?

6 People knew that the circumference is about 3 times the diameter but they wanted to find out exactly. C = ? x d C ≈ 3 x d This means APPROXIMATELY EQUAL TO

7 The exact true value is…………… UNKNOWN!!

8 An approximation to π π≈ forever….

9 What about the AREA of a circle? 2r r First consider a square The area of this square in terms of r is A= 2r x2r = 4r 2

10 What about the AREA of a circle? 2r Now consider a circle inside the square The area of the circle must be less than the are of the square A < 4r 2 r Area = ? xr 2

11 Finding a formula for the area of a circle

12 C= πd or C=2πr Semi-circle=πr πrπr r

13 Area of Rectangle= Base x Height Area = πr x r Area =πr 2

14 The Area and Perimeter of a Circle A circle is defined by its diameter or radius Diameter radius The perimeter or circumference of a circle is the distance around the outside The area of a circle is the space inside it The ratio of π (pi) π is an irrational number whose value to 15 decimal places is π = We usually say π≈3.14 The circumference is found using the formula C=π d or C= 2πr (since d=2r) The area is found using the formula A=πr 2

15 The Area and Perimeter of a Circle A circle is defined by its diameter or radius Diameter radius The perimeter or circumference of a circle is the distance around the outside The area of a circle is the space inside it The ratio of π (pi) π is an irrational number whose value to 15 decimal places is π = We usually say π≈3.14 The circumference is found using the formula C=π d or C= 2πr (since d=2r) The area is found using the formula C=πr 2

16 Videos on Circles A Rap about circles Dw0&feature=related


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