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JEE Previous Year Question

$The rate of change of area of a circle with respect to its radius at r = 2 cms is$

Topic: JEE PYQ

Answer: D. Full step-by-step solution below.

A $4$
B $2 π$
C $2$
D $4 π$

Correct answer: D

Solution

(d) : Area of circle, A = π r^{2} (i) Differentiate (i) w.r.t. r, we get \frac{dA}{dr} = 2 πr ∴ (\frac{dA}{dr})_{r = 2} = 2 π (2) = 4 π

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