3. (10 %) Find the area of the surface formed by revolving the polar equation r = 2 cos θ over the interval about the line r = 5 secθ.

(13) A logistic population model with relative growth rate 0.1 per year and carrying capacity 50 thousand can be expressed by the differential equation =0.1P(1 - ), with P in thousands and t in years. Given that the initial population is 9 thousand. Find the population size after 20 years. (If you memorized the formula, then you need to derive it for this problem.)

3. (10 %) Find the area of the surface formed by revolving the polar equation r = 2 cos θ over the interval about the line r = 5 secθ.

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