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Warm-Up’s
Warm-Up’s
2.
Warm-Up’s
The circumference and Area of a circle
Diameter
Radius
centre
What is the formula
relating the circumferenc
e to the diameter?
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
An approximation to π
π≈3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067982148086513282306647093844609550582231725359408128481117450284102701938521105559644622948954930381964428810975665933446128475648233786783165271201909145648566923460348610454326648213393607260249141273724587006606315588174881520920962829254091715364367892590360011330530548820466521384146951941511609................forever….
What about the AREA of a circle?2r
2rr
First consider a square
The area of this square
in terms of r is
A= 2r x2r = 4r2
What about the AREA of a circle?2r
2r
Now consider a circle inside the square
The area of the circle must be less than the are of the square
A < 4r2
r
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 CircleA circle is defined by its diameter or radius
Diameter
radi
usThe 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)diameter
ncecircumfere
π is an irrational number whose value to 15 decimal places is π = 3.14159265358979.... We usually say π≈3.14The 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 CircleA circle is defined by its diameter or radius
Diameter
radi
usThe 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)diameter
ncecircumfere
π is an irrational number whose value to 15 decimal places is π = 3.14159265358979.... We usually say π≈3.14The 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
