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The radius of a circle grows at 2 cm/s. How fast is the area increasing when the radius is 5 cm?
A40π cm²/s
B20π cm²/s
C25π cm²/s
D10π cm²/s
Answer & Solution
Correct answer: B. 20π cm²/s
dA/dt = 2πr dr/dt = 2π(5)(2) = 20π cm²/s.
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