Question

Find the rate of change of the area of a circle with respect to its radius ‘r’ when r = 4 cm.

Answer 1

If A is area and r is the radius of a circle, then

A = πr²

⇒ \(\frac{dA}{dr}\) = 2πr

∴ \(\begin{bmatrix} \frac{dA}{dr} \end{bmatrix}_{r=4}\) = 8π cm²/cm