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प्रश्न
The radius of a circle is increasing at the rate of 0.7 cm/s. What is the rate of increase of its circumference?
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उत्तर
Let us assume that radius of the circle = r.
Given `(dr)/dt = 0.7` cm/s
Area of a circle C = 2`pi`r
The rate of change of c with respect to t,
`(dC)/(di) = 2 pi (dr)/dt`
`= 2pi (0.7) = 1.4 pi`
Hence, the rate of increase of circumference (1.4 π) cm/sec.
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