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The radius of a circular ripple made by dropping a stone into a pond is increasing at a rate of 8cms⁻¹. Find the rate at which the area is increasing when the radius is 25cm. Leave answer as an amount of pi, is the answer is 69π put in the answer box: 69 Dont include units in the answer. Hint: Answer is in cm²s⁻¹

 

http://www.itstoohard.com/puzzle/m08XehEu

Guest Oct 30, 2017
edited by Guest  Oct 30, 2017
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dr/dt = 8 cm/s

 

A = pi*r2 so dA/dt = 2pi*r*dr/dt

 

A = 2pi*25*8 cm2/s → 400pi cm2/s

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Alan  Oct 30, 2017

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