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104 台聯大微積分(A2) 第 11 題

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104學年度 · 104微積分A2 · 第 11 題

題目

Problem

3. A manufacturer finds that it takes xx units of labor and yy units of capital to produce f(x,y)=100x3/4y1/4f(x,y)=100x^{3/4}y^{1/4} units of product. If a unit of labor costs $100, a unit of capital costs $200, and $200,000 is budgeted for production, determine how many units should be expended on labor and how many units should be expended on capital in order to maximize production.

解答

預算限制為 100x+200y=200000100x+200y=200000,即 x+2y=2000x+2y=2000。令 x=2000−2yx=2000-2y,極大化

f4=1004(2000−2y)3y.f^4=100^4(2000-2y)^3y.

其導數為常數倍  (2000−2y)2(2000−8y)\,(2000-2y)^2(2000-8y),故 y=250y=250、x=1500x=1500。答案為

x=1500 單位勞力,y=250 單位資本.\boxed{x=1500\text{ 單位勞力},\quad y=250\text{ 單位資本}}.