The Post Office used to have a strange way of limiting the size of packages. The maximum allowed was a 2 meters combined length and girth. Given this restriction, what is the greatest volume of a package that is shaped like a rectangular prism with whole centimeter dimensions? (Remember that 100 cm = 1 m)

Respuesta :

Answer:

[tex]V=74,052\ cm^3[/tex]

Step-by-step explanation:

we know that

The maximum volume for a rectangular prism is when the base is a square

The girth is the distance around the package perpendicular to the length

see the attached figure to better understand the problem

Let

x ----> the length of the square base of the prism

h ---> the height of the prim

we have that

[tex]4x+h=2[/tex]

[tex]h=2-4x[/tex] -----> equation A

The volume of a rectangular prism is given by

[tex]V=Bh[/tex]

where

B is the area of the base

h is the height of the prism

we have

[tex]B=x^2[/tex]

so

[tex]V=x^2h[/tex] ----> equation B

substitute equation A in equation B

[tex]V=x^2(2-4x)[/tex]

[tex]V=-4x^3+2x^2[/tex]

Find the first derivative of the function

[tex]\frac{dV}{dx}=-12x^2+4x[/tex]

equate to zero

[tex]-12x^2+4x=0\\-12x(x-\frac{1}{3})=0[/tex]

[tex]x=0.33\ m[/tex] ---->[tex]x=33\ cm[/tex]

[tex]h=200-4(33)=68\ cm[/tex]

therefore

The greatest volume  is equal to

[tex]V=(33^2)(68)=74,052\ cm^3[/tex]

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