Question

A 1125 ft^3 open-top rectangular tank with a square base x ft on a side and y ft deep is to be built with its top lush with the ground to catch runoff water. The costs associated with the tank involve not only the material from which the tank is made but also an excavation charge proportional to the product xy.a. If the total cost isc = 5(x^2 + 4xy) + 10xy,what values of x and y will minimize it?b. Give a possible scenario for the cost function in part (a).

Answer 1

Answer:

The values of x and y that will minimize the cost is 15 ft and 5 ft respectively and the minimum cost will 3,375

Step-by-step explanation:

With a 1125 ft^3 open-top rectangular tank with a square base x ft on a side and y ft deep is to be built with its top lush with the ground to catch runoff water, x is the length, y is the height;

x^2*y = 1125

y = 1125/x^2 ----(1)

The total cost of c = 5(x^2 + 4xy) + 10xy

Then,

c = 5(x^2 + 4x*(1125/x^2)} + 10x*(1125/x^2)

c = 5x^2 + 22,500/x + 11,250/x

c = 5x^2 + 33,750/x

To minimize the cost of c, find the derivatives of c; c'

c' = 10x - 33,750/x^2

c' = (10x^3 - 33,750)/x^2

c'(x) = 0; 10x^3 = 33,750

x = ³√33,750 = 15

x = 15; y = 1125/x^2

y = 1125/15^2 = 5

(x,y) = (15,5)

c = 5x^2 + 33,750/x

c = 5*15^2 + 33,750/15 = 3,375

The values of x and y that will minimize it is 15 ft and 5 ft respectively and the minimum cost will 3,375