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Area and Circumference of a Circle

Area – number of square units enclosed in the circle

$A=\pi r^{2}$

Circumference – distance around the circle

$C=\pi\times d$

$\pi\ (Pi)=3.14\ (constant)$

diameter = 2⋅radius

If a circle has a circumference of 15.7 cm, what is the area?

$C=\pi\times d$

$\frac{C}{\pi}=\frac{\pi\times d}{\pi}$

$d=\frac{C}{\pi}$

$d=\frac{15.7\ cm}{3.15}$

$d=5\ cm$

$d=2\times r$

$r=\frac{d}{2}$

$r=\frac{5\ cm}{2}$

$r=2.5\ cm$

$A=\pi\times r^{2}$

$A=(3.14)(2.5\ cm)^{2}$

$A=19.625\ cm^{2}$