A storage shed is to be built in the shape of a box with a square base. It is to have a volume of 729 cubic feet. The concrete for the base cost $8 per square foot, The material for the roof costs $3 Per square foot, and the material for the sides costs $5.50 Per square foot. Find the dimensions of the most economical shed.

Respuesta :

The dimensions of the most economical shed are 9 ft in length, 9 ft in width, and 9 ft in height if the storage shed is to be built in the shape of a box with a square base.

What is volume?

It is defined as a three-dimensional space enclosed by an object or thing.

It is given that:

A storage shed is to be built in the shape of a box with a square base.

It is to have a volume of 729 cubic feet.

Let x be the length of the base

Let y be the height of the box.

V = 729 cubic feet

The base is square:

l = w = x

V = x²y

y =  729/x²

Cost of the base = $8x²

Cost of the roof = 3x²

Cost of the sides = 4(5.50)xy

= 22xy

Total cost

C= 8x² + 3x² + 22xy

C = 11x² + 22x(729/x²)

C = 11x² + 16038/x

Find the first derivative:

dC/dx = 22x - 16038/x²

Equate; dC/dx = 0

22x - 16038/x² = 0

22x = 16038/x²

22x³ =16038

x³ = 729

x = 9

y = 729/(9)² = 9

Length of base = 9 ft

Width of base  = 9 ft

Height of box = 9 ft

Thus, the dimensions of the most economical shed are 9 ft in length, 9 ft in width, and 9 ft in height.

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