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Warm-Up’s

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Warm-Up’s 2.

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Warm-Up’s

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**The circumference and Area of a circle**

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**What is the formula relating the circumference to the diameter?**

centre Diameter Radius

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**This means APPROXIMATELY EQUAL TO**

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

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**The exact true value is……………**

UNKNOWN!!

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An approximation to π π≈ forever….

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**What about the AREA of a circle?**

First consider a square The area of this square in terms of r is A= 2r x2r = 4r2 r 2r

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**What about the AREA of a circle?**

Now consider a circle inside the square The area of the circle must be less than the are of the square A < 4r2 2r r 2r Area = ? xr2

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**Finding a formula for the area of a circle**

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C= πd or C=2πr Semi-circle=πr πr r

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**Area of Rectangle= Base x Height**

Area = πr x r Area =πr2

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**The Area and Perimeter of a Circle**

A circle is defined by its diameter or radius radius The perimeter or circumference of a circle is the distance around the outside The area of a circle is the space inside it Diameter 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=πr2

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**The Area and Perimeter of a Circle**

A circle is defined by its diameter or radius radius The perimeter or circumference of a circle is the distance around the outside The area of a circle is the space inside it Diameter 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=πr2

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**Videos on Circles A Rap about circles**

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