1. The radius of a sphere is r inches at time t seconds. Find the radius when the rates of increase of the surface area and the radius are numerically equal.

Question

A
1/4π in
B
1/5π in
C
1/3π in
D
1/8π in
E
1/2π in

Answer 1

a = 4πr^2
da/dt = 8πr dr/dt
if the rates are the same,
1 = 8πr, so r = 1/(8π)
So, (D)

Answer 2

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Answer 3

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Answer 4

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Answer 7

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Answer 9

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Answer 10

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