# The rate of change of an area of a circle with respect to its radius which is 7 cms is

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The rate of change of an area of a circle with respect to its radius which is 7 cms is
1. 21π
2. 14π
3. 7π
4. 12π

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Correct Answer - Option 2 : 14π

Concept:

Rate of change of 'x' with respect to 't' is given by $\rm \frac {dx}{dt}$

Calculation:

Given r = 7cms

Area of a circle A = π r2

$\rm {dA \over dr}$ = 2πr

At r = 7cms

$\rm {dA \over dr}$ = 2π × 7

$\rm {dA \over dr}$ = 14π