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Of all closed rectangular boxes of volume 64 ft3, what is the smallest surface area?

Sagot :

The smallest surface area of cubic rectangular boxes = 96 ft²

What is surface area?

An object with three dimensions is solid and has both height and depth. A sphere and a cube, for instance, have three dimensions, whereas a circle and a square do not.

A three-dimensional shape's total surface area equals the sum of its side's surface areas. The measured area of all surfaces of three-dimensional solids, such as cubes, spheres, prisms, and pyramids, is expressed in square units.

Since it is a closed rectangular box so, there will be two equal sides.

According to the given Information:

Volume = 64 ft³

Volume of rectangular cube = hx²

Surface area of rectangular cube = 2x²+4hx

Equating the above equation we get, hx² = 64

                                                               h=64/x²

Put the value of h in surface area formula,

S = 2x² + 4(64/x²)*x

S = 2x² + 256/x

For the surface area to be minimum,

ds/dx = 0

4x - (256/x²) = 0

4x³ = 256

x³ = 64

x = 4 ft

Therefore, the smallest surface area

= 2(4)² + (256/4)

S = 32 + 64

= 96 ft²

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