Warm-Up’s

Warm-Up’s 2.

Warm-Up’s

The circumference and Area of a circle

What is the formula relating the circumference to the diameter? centre Diameter Radius

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

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

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

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

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

Finding a formula for the area of a circle

C= πd or C=2πr Semi-circle=πr πr r

Area of Rectangle= Base x Height Area = πr x r Area =πr2

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 = 3.14159265358979.... 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

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 = 3.14159265358979.... 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

Videos on Circles A Rap about circles http://www.youtube.com/watch?v=fogehnFNDw0&feature=related