※ 引述《s1990716 (小婷)》之銘言： : 1.Marginal Profit : When the price of a glass of lemonade at a lemonade stand was $1.75, : 400 glasses were sold. When the price was lowered to $1.50, 500 glasses : were sold. Assume that the demand function is linear and that the variable : and fixed cost are $0.10 and $25,respectively. variable and fixed cost? 先了解定義才能做 : Find the profit P as a function of x,the number of glasses of lemonade sold. 這一題不確定題意是不是這樣 我的理解是這樣 total cost c = 0.1x + 25 demand function is $ = $(x) 1.75 = 400a + b 1.50 = 500a + b => a = -0.0025 b = 2.75 P = x*$ - c = x*(-0.0025x + 2.75) - (0.1x + 25) : 2.Depreciation : The value V of a machine t years after it is purchased is inversely : proportional to the square root of t+1. The initial value of the machine is : $10,000. : a.Write V as a function of t V = a / (t+1)^2 t = 0 , V = 10000 => V = 10000 / (t+1)^2 : b.Find the rate of depreciation when t=1 Rate(t) = dV/dt = -20000 / (t+1)^3 Rate(t=1) = -20000 / 8 = -2500 ($/yr) (minus sign means depreciation) : 煩請各位高手解惑~~~ --

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