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The radius of a circle is increasing at ...

The radius of a circle is increasing at the rate of 0.7 cm/sec. What is the rate of increase of its circumference?

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Let r be the radius and C be the circumference of circle.
Given `(dr)/(dt) = 0.7 cm//sec`
Now ` C = 2 pi r`
`rArr (dC)/(dt) = 2pi (dr)/(dt)`
`-2pi xx 0.7 = 1.4 pi cm//sec`
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NAGEEN PRAKASHAN ENGLISH-APPLICATIONS OF DERIVATIVES-Exercise 6.1
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