Find the rate of change of the area of a circular disc with respect to its circumference when the radius is 3 cm.

Explanation

Let `A` be the area of the circular disc. Then,



`A=pi r^{2} `


`Rightarrow frac{d A}{d r}=2 pi r`



Let `C` be the circumference of the circular disc. Then,



`C=2 pi r`


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