For any circle with radius r:
Area: A=πr2
Circumference: C=2πr
To find dCdA, use the chain rule:
dCdA=dC/drdA/dr
Finding drdA:
A=πr2
drdA=2πr
Finding drdC:
C=2πr
drdC=2π
dCdA=dC/drdA/dr
dCdA=2π2πr
dCdA=r
At r=4 cm:
dCdA=4 cm
Therefore, the rate of change of area with respect to circumference is 4 cm.