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The rate of change of the area of a circle with respect to its radius $r$ at $r=6 \mathrm{~cm}$ is
(a) $10 \pi$
(b) $12 \pi$
(c) $8 \pi$
(d) $11 \pi$
The rate of change of the area of a circle with respect to its radius $r$ at $r=6 \mathrm{~cm}$ is
(a) $10 \pi$
(b) $12 \pi$
(c) $8 \pi$
(d) $11 \pi$
Solution:
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Verified Answer
(b) $\because \mathrm{A}=\pi \mathrm{r}^2 \Rightarrow \frac{\mathrm{dA}}{\mathrm{dr}}=2 \pi \times 6=12 \pi \mathrm{cm}^2 /$ radius.
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