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Area and Circumference of a Circle
供稿人: Adam Mlynarczyk
Area = π×r2
Area and Circumference of a Circle
r - radius
Circumference = π×d
d - diameter
From the picture we seethat the radius r=6cm, sowe can easily find area, byusing the area formula:
A=π×r2=πx62=π×36=113.1cm2 (1 d.p.)
Calculate Area of this Circle
6cm
For number π, please usecalculator or substitute π≈3.142
From the picture we see that the radius r=6cm, but for 
circumference we need diameter, but of course d=2r,
so diameter here will be d=2 x 6cm=12cm and now
we can easily find circumference, by using the formula:
C=π×d=πx12=37.7cm (1 d.p.)
Calculate Circumference of this Circle
diameter
For number π, please usecalculator or substitute π≈3.142
6cm
A=π×r2=π×    =     cm2
Calculate Area of this Circle
Remember r2=r x r
For number π, please usecalculator or substitute π≈3.142
5cm
Round the answer 
to 1 decimal place
C=π×d=π×    =     cm
Calculate Circumference of this Circle
diameter
For number π, please usecalculator or substitute π≈3.142
Remember d=2 x r
5cm
Length of the Arc
and Area of the Sector
Asector = angle/360  x πr2
Arc
Length of Arc = angle/360 x πd
This is formula for the area of the wholecircle, so to find thearea of the sector multiply it by thefraction angle/360.
Remember d = 2 x r
This is formula for the circumeferenceof the whole circle, so to find length ofthe arc we need to multiply it by thefraction angle/360.
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