Find the rate of change of the area of a circle with respect to its ra

1.	Find the rate of change of the area of a circle with respect to its radius r when(a) `r = 3 c m` (b) `r = 4 c m`
Answer» Let radius of circle be r and area be A. Area A = `pi r^(2)` `rArr (dA)/(dr) = pi (2r)` (a) at r = 3 cm ` (dA)/(dr) = pi xx 2 xx 3 = 6 pi cm^(2)//sec` (b) at r = 4 cm ` (dA)/(dr) = pi xx 2 xx 4 = 8 pi cm^(2) //sec`

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Find the rate of change of the area of a circle with respect to its radius r when(a) `r = 3 c m` (b) `r = 4 c m`

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