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7. A stone is dropped into a quiet lake and waves move in circles at a speed of 2cm per second. At the instant, when the radius of the circular wave is 12 cm, how fast is the enclosed area changing ?
A. Decreasing at the rate of 48π cm2 / sec
B. Increasing at the rate of 24π cm2 / sec
C. Increasing at the rate of 48π cm2 / sec
D. Decreasing at the rate of 24π cm2 / sec
10. Given a function y = f(x) . Let Δx be the very small change in the value of x , then the corresponding change in the value of y that is Δy is approximately given by
A. A
B. B
C. C
D. D
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