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Circles

Circles. Objective: To find the circumference and area of a circle. The circumference of a circle is. The distance around a circle. Hint: Circumference: remember circle around. What is the formula relating the circumference to the diameter?. circumference. center. Diameter. Radius.

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Circles

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  1. Circles Objective: To find the circumference and area of a circle.

  2. The circumference of a circle is The distance around a circle Hint: Circumference: remember circle around

  3. What is the formula relating the circumference to the diameter? circumference center Diameter Radius

  4. An approximation to π π≈3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067982148086513282306647093844609550582231725359408128481117450284102701938521105559644622948954930381964428810975665933446128475648233786783165271201909145648566923460348610454326648213393607260249141273724587006606315588174881520920962829254091715364367892590360011330530548820466521384146951941511609................forever….

  5. Two formulas are used in finding the circumference of a circle. WHEN THE CIRCLE HAS A DIAMETER MEASUREMENT, USE THE FOLLOWING FORMULA. C = d When the radius of a circle is given, the following formula should be used. C= 2 r

  6. EXAMPLE #1 FIND THE CIRCUMFERENCE OF THE CIRCLE. Circumference = d 3.14 x 4in. 12.6in. 4in.

  7. EXAMPLE #2 FIND THE CIRCUMFERENCE OF THE CIRCLE. Circumference = 2 r 2 x 3.14 x 5cm 31.4cm 5 cm HINT: Always round your answers to the nearest tenth.

  8. Circumference (It Just Makes Sense) ChorusIf I need to measure up a clock (circumference)Measure the post on a dock (circumference)If I’m buying rims for a car (circumference)Hey, yo, 2πr! (It just makes sense)If I need to measure up a hat (circumference)Spinnin’ records like that (circumference)If I need to pick the right jar (circumference)Hey, yo, 2πr! (It just makes sense) Verse ICheck out and see all the round things you can findSo many circles out there, it will blow your mindIt can be hard to measure distance aroundBut once you use a little math you can figure it outIf you need to find the distance around a circle shapeAll you need is one formula and a measuring tapeThen you measure up the radius so you can figure out‘Cause twice that radius times π is what a circle’s all about Chorus Verse IIYou know that every circle—if it’s big or little—Has one single point that’s right in the middleSo you start on one edge, draw a straight lineRight through the center and to the other sideThat’s the diameter. And half of that is the radiusThat’s the crucial number that we need to figure this outThen we multiply it by 2πCircumference, 2πr, there’s no need to ask why

  9. PRACTICE #1 8 ft. 25.1 ft 1. Find the circumference. 2. Find the circumference of a circle with a radius of 5 cm. 31.4 cm

  10. AREA FILLING THE CIRCLE. A = r² r

  11. EXAMPLE #1 Find the area of the circle. ● A = r² A = 3.14(2)² A = 3.14(4) A = 12.56 in² 2 in

  12. EXAMPLE #2 ● Find the area of the circle. A = r² A = 3.14(10)² A = 3.14(100) A = 314 cm² 20 cm

  13. PRACTICE #2 Find the area of the following circles. 2. 1. ● A = r² ● A = r² A =3.14 (1.5)² 3 yd A = 3.14 (7.5)² 7.5 mi A = 3.14 (2.25) A = 3.14 (56.25) A = 7.1 yd² A = 176.6 mi²

  14. Area and Circumference of a Circle Song This song is sung to the tune of the Wheels on the Bus The area of a circle is Pi r squaredPi r squaredPi r squaredThe area of a circle is Pi r squaredAll through the circles The circumference of a circle is 2 pi r2 pi r2 pi rThe circumference of a circle is 2 pi rAll around the circle

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