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The region inside a circle expands at 6π cm²/s. Find the circumference's growth rate at r = 3 cm.
A6π cm/s
B2π cm/s
C3π cm/s
Dπ cm/s
Answer & Solution
Correct answer: B. 2π cm/s
2πr(dr/dt) = 6π gives dr/dt = 1, so the circumference 2πr grows at 2π cm/s.
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