Express the area A of a circle as a function of its circumference C.?

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Express the area A of a circle as a function of its circumference C.?
A = πr²


C = 2πr





Solve the second equation for r:





r = C / 2 π





Substitute:





A = π (C / 2π) ²





= π C² / (4 π²)





= C² / (4π)
Reply:Wow. Alot of votes for that answer that was nonsense (the point is to eliminate the variable r, or else it is not a function of C). Report It

Reply:A = pi r^2......(1)


C = 2pi*r, =%26gt; C^2 = 4pi^2*r^2......(2)


(1)/(2): A/C^2 = 1/(4pi) =%26gt; A = C^2/(4pi)


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Ideas to save time: Square the second equation.
Reply:(circumference / diameter ) * (radius*radius)
Reply:A=π r²


C=2π r


π r²=(2π r)(r/2)


A=C(r/2)
Reply:A = pi*r^2


C = 2*pi*r





A = pi*[C/2*pi]^2


=C^2 / (4*pi^2)