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A ripple's edge moves at 5 cm/s. At radius 8 cm, the enclosed area increases at what rate?
A160π cm²/s
B80π cm²/s
C64π cm²/s
D40π cm²/s
Answer & Solution
Correct answer: B. 80π cm²/s
dA/dt = 2πr(dr/dt) = 2π × 8 × 5 = 80π cm²/s.
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