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A ring is dropped into a quiet pond and waves move in circles at a speed of 2 cm/second. At the instant, when the radius of the circular wave is 12 cm, how fast is the enclosed area increasing?

Solution

✅ Correct Option: 3

With A=πr2A=\pi r^2, dAdt=2πrdrdt=2π(12)(2)=48π\dfrac{dA}{dt}=2\pi r\dfrac{dr}{dt}=2\pi(12)(2)=48\pi. Area is measured in square units, so the rate is 48π cm2/sec48\pi\ cm^2/sec.

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