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

Explanation

Let radius of the disc be `r`


Thus it's area `A=pi r^{2}` and circumference `S=2 pi r`


Now `frac{d A}{d r}=2 pi r, frac{d S}{d r}=2 pi therefore frac{d A}{d S}=r`


Hence rate of change of area of disc w.r.t circumference at `r=3 cm` is `=3 cm`.