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# Solution for Find the Rate of Change of the Area of a Circular Disc with Respect to Its Circumference When the Radius is 3 Cm ? - CBSE (Commerce) Class 12 - Mathematics

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ConceptRate of Change of Bodies Or Quantities

#### Question

Find the rate of change of the area of a circular disc with respect to its circumference when the radius is 3 cm ?

#### Solution

Let A be the area of the circular disc. Then,

= $\pi r^2$

$\Rightarrow \frac{dA}{dr} = 2\pi r$

Let C be the circumference of the circular disc. Then,

C = $2\pi r$

$\Rightarrow \frac{dC}{dr} = 2\pi$

$\therefore \frac{dA}{dC} = \frac{\frac{dA}{dr}}{\frac{dC}{dr}}$
$\Rightarrow \frac{dA}{dC} = \frac{2\pi r}{2\pi} = r$
$\Rightarrow \left( \frac{dA}{dC} \right)_{r = 3} = 3 cm$

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Solution Find the Rate of Change of the Area of a Circular Disc with Respect to Its Circumference When the Radius is 3 Cm ? Concept: Rate of Change of Bodies Or Quantities.
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