Question

The rate of change of area of a circle with respect to its radius is
(aj 4πr
(b) 3πr
(c) 2πr
(d) none of these​

Answer 1

Answer:

(c)

$\: a \: = \pi {r}^{2} \\ \frac{da}{dr \: } = 2\pi \: r \: \\ (differentiate \: wrt \: r)$