題組內容

2. A farmer is engaged in ploughing the fields. He buys a mini cultivator for 200 dollars, incurs a cultivation cost flow at a rate of G(t) = 0.4t dollars per year during the life of the cultivator, and sells it at t = T for R(T) = 4 + 20T - T 2 dollars. The market rate of interest is 20%. Please answer the following 2 questions:

(2)Also verify that your solution is a maximum. (10%)